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.
Very interesting idea for the frosting.
Oh, yeah…. My kids and hubby would be thrilled with these!
These are very beautiful!
I really like the coloring
People who scrape the frosting off are just odd. I LOVE frosting too!
Great job on this frosting, Aimee! And the bars sound fabulous. The texture looks dreamy.
What a fun spring time treat. I will definitely have to make these. Love your blog and I am your newest follower. xo
These look so cool. Who knew??!! And I’m right there with you on the frosting. That’s almost the best part!
these are too cute! i’m adding them to my to-bake list. i love all those colors! awesome recipe. 🙂
First off: M & M cookie bars = win!
The rainbow decoration looks great! 🙂
Those are so pretty! Love what you’ve done with the frosting … I am not the biggest, best froster, but I think I need to try that technique. Sometime.
They look awesome, your frosting turned out so well! I just love the technique – such an impressive result and really not too difficult 🙂
Wonderful recipe! I thik I’ll make this for Hubby tonight to take to twork. His co-workers are chocolate chip M&M fans!
I love the rainbow icing–so gorge! And M&M cookie bars are my favorite.
I love all those features! Thanks so much for hosting.
I love that frosting! I have never seen one with meringue powder and butter. It sounds SO good. I will be trying it for sure!
I love the rainbow frosting! It’s so pretty and looks so intricate. I don’t have the patience to do that but I really want to now seeing yours!
These are gorgeous–love that rainbow frosting!
Frosting or no frosting…they both look good!
I have a couple in our house that scrape the yummy frosting off. But you are right…more for us:-) Love the fun rainbow icing!!!!
These are so pretty!! Awesome job. I love that icing 🙂