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Rainbow M&M'S Cookie Bars Recipe

Rainbow Cookie Bars: delicious chocolate chip cookie bars topped with a rainbow buttercream (tutorial).

Prep Time
15 mins
Total Time
15 mins
Servings: 24 bars
Calories: 174 kcal
Course: Baked Goods
Cuisine: American

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

    Cup of Yum
  1. For the cookies, bake and cool one batch of chocolate chip cookie bars.
  2. Start by making your basic white buttercream frosting.
  3. 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.
  4. 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.
  5. Add powdered sugar, milk, and pure vanilla extract.
  6. Beat an additional 3-5 minutes until light and fluffy.
  7. Now decide how many colors in your rainbow!
  8. I chose four pastel colors for my spring cookies!
  9. 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.
  10. Spoon frosting into small 12-inch disposable frosting bags. Snip off the tips.
  11. Carefully slide all four bags into a LARGER frosting bag. I used an 18-inch bag with star tip attached.
  12. Pipe frosting onto cooled cookie bars!

Notes

  • 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.
  • 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.

Nutrition Information

Calories 174kcal (9%) Carbohydrates 26g (9%) Fat 8g (12%) Saturated Fat 5g (25%) Polyunsaturated Fat 3g Cholesterol 21mg (7%) Sodium 7mg (0%) Sugar 25g (50%)

Nutrition Facts

Serving: 24bars

Amount Per Serving

Calories 174

% Daily Value*

Calories 174kcal 9%
Carbohydrates 26g 9%
Fat 8g 12%
Saturated Fat 5g 25%
Polyunsaturated Fat 3g 18%
Cholesterol 21mg 7%
Sodium 7mg 0%
Sugar 25g 50%

* Percent Daily Values are based on a 2,000 calorie diet.