Soft and chewy M&M Cookie bars topped with a sweet rainbow buttercream frosting. These frosted Rainbow M&M Cookie Bars are dreamy and delicious!
Love cookie bars? These Peanut Butter Chocolate Chip Bars are gooey and delicious with puddles of peanut butter! Or try our favorite Frosted Sugar Cookie bars for an treat!
Why this Recipe Works
I love frosting.
While some of my family scrapes the extra frosting off their cake, I pile it on to my slice.
- A good buttercream frosting
- Rainbow colors.
- It also sits on top of a delicious, soft and chewy, M&M Cookie bar.
If you love rainbow treats, give our rainbow frosting board a try next. You can even add some of today’s cookie bars to the board!
How to Make Rainbow Frosting
Start by making your basic white buttercream frosting.
I make a larger batch so that I can put a decent sized “rainbow” on each individual cookie bar (or cupcake!). You can cut the batch in half if you think you prefer less frosting.
Begin by beating softened butter for about 3 minutes using an electric mixer with whisk attachment. Scrape down the sides of the bowl as needed, until you see the butter turn pale in color, and smooth.
Add powdered sugar, milk, and pure vanilla extract.
Beat an additional 3-5 minutes until light and fluffy.
Now decide how many colors in your rainbow!
PRO TIP: Use Americolor gel colors for more vibrant colors that require less drops. Each of my colors was ONE drop of gel.
I chose four pastel colors for my spring cookies!
Separate your frosting into small bowls (for each color). Add one drop of gel coloring to each bowl, stir until no white frosting is seen. Add more color if desired.
Spoon frosting into small 12-inch disposable frosting bags. Snip off the tips.
Carefully slide all four bags into a LARGER frosting bag. I used an 18-inch bag with star tip attached.
Pipe frosting onto cooled cookie bars!
This is also very pretty piped onto cupcakes!
Can I freeze frosting?
Yes!
Frosting will stay good in the refrigerator for 4-5 days.
However, should you choose to freeze frosting, it can keep in an airtight container for up to 3 months in the freezer.
Thaw frosting overnight in the refrigerator.
You may need to beat it again with your mixer to get it light and fluffy, and you may need to add 1-2 TBSP of milk too.
What can I do with leftover frosting?
Help! This was too much frosting for me.
While I personally don’t understand that phrase, I do know that some people don’t like as much frosting as I do.
In addition to freezing frosting, you can also pipe it onto sugar cookies for a delicious treat.
Or add frosting to these Bakery style brownies.
Still not sure how to use your leftover frosting?
Make a batch of Buttercream Truffles. That’s right, sweet candy made from your LEFTOVERS. Dream come true!
More Rainbow Desserts
My family loves these soft and chewy M&M Cookies. They’re basically M&M Chocolate Chip, with a delicious chewy texture!
These Rainbow Chip Brownies are made using the best homemade buttermilk brownie recipe! Move over Cosmic Brownies from Little Debbie…these are too delicious to compare!
You’ll love these decadent Rainbow Fudge Cookie Bars. Chocolate Chip Cookie bars topped with a sweet fudge and rainbow chips!
More Easy Dessert Recipes
- Double Chocolate Chip Cookies
- Shortbread Cookies
- Snickerdoodles
- Flower Pretzel Candy
- Banana Pudding
- Sugar Cookie Frosting
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Rainbow M&M’S Cookie Bars Recipe
Equipment
Ingredients
- 1 batch M&M Cookie Bars
For the Frosting:
- 1 cup unsalted Butter softened
- 5 ½ cups powdered sugar
- ¼ cup milk
- 2 teaspoons vanilla extract
- gel food coloring
Instructions
- For the cookies, bake and cool one batch of chocolate chip cookie bars.
- Start by making your basic white buttercream frosting.
- I make a larger batch so that I can put a decent sized "rainbow" on each individual cookie bar (or cupcake!). You can cut the batch in half if you think you prefer less frosting.
- Start by beating softened butter for about 3 minutes using an electric mixer with whisk attachment. Scrape down the sides of the bowl as needed, until you see the butter turn pale in color, and smooth.
- Add powdered sugar, milk, and pure vanilla extract.
- Beat an additional 3-5 minutes until light and fluffy.
- Now decide how many colors in your rainbow!
- I chose four pastel colors for my spring cookies!
- Separate your frosting into small bowls (for each color). Add one drop of gel coloring to each bowl, stir until no white frosting is seen. Add more color if desired.
- Spoon frosting into small 12-inch disposable frosting bags. Snip off the tips.
- Carefully slide all four bags into a LARGER frosting bag. I used an 18-inch bag with star tip attached.
- Pipe frosting onto cooled cookie bars!
Notes
- Use Americolor gel colors for more vibrant colors that require less drops. Each of my colors was ONE drop of gel.
- Frosting will stay good in the refrigerator for 4-5 days.
- However, should you choose to freeze frosting, it can keep in an airtight container for up to 3 months in the freezer.
- Thaw frosting overnight in the refrigerator.
- You may need to beat it again with your mixer to get it light and fluffy, and you may need to add 1-2 TBSP of milk too.
Yep, I just made some on Saturday because of that post. It’s amazing!
These bars are a DREAM! And that rainbow frosting is great! Perfect for parties!
We love m&m cookie bars & the addition of the cute frosting on top, would make them even better! My girls are all about rainbows!
These look perfectly decadent! I will have to make these for my daughter’s birthday party, she will love them!
These are just what I was looking for! Adding these to the birthday party menu.
These cookie bars were a hit around here! My daughters made them and frosted according to your tips. Cutest treat ever!
I need help…i baked your recipe for blondies the other day…they were still raw…i rebaked them for another 20 min and still so soft u cant pick them up…i followed recipe exactly and i still cannot seem to find a good bkondie that is “chewy” without being sloppy raw like…
Hmm. Not sure what to tell you. I’ve been making that blondies recipe for years with no issue 🙁
These are so colorful and I love the recipe for the basic cookie bar!You are a party fave this week at the {what’s shakin’ link party} … I’d love for you to come on over, link up and grab a button!
These look so delicious! We’re so glad that you linked up to our “Strut Your Stuff Saturday.” We hope you’ll be back soon. -The Sisters
As a child of the 70s I can never resist a rainbow, especially one as “sweet” as yours!
Jenn
Oh my goodness these look so yummy! I followed you over from Chef-in-Training and would like to invite you to share this, and any other posts, on my link party at www.michellestastycreations.blogspot.com. Have a great weekend.
Hugs,
Michelle
That looks terrific. I know my family would love this. Come visit us. We have some fantastic things to share this week.
Plain M&Ms are one of my biggest weaknesses. I love putting them in cookies and bars!
I love cookie bars but have never frosted them. Looks like I better frost the next batch. Great recipe.