Step 1: Preheat Your Oven - Start by preheating your oven to 350°F (175°C) for even baking.
Step 2: Cream the Butter and Sugars - In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy (about 2-3 minutes).
Step 3: Add the Eggs and Vanilla - Beat in the egg, egg yolk, and vanilla extract until smooth and creamy.
Step 4: Combine the Dry Ingredients - In another bowl, whisk together the flour, baking soda, and salt. Gradually mix this into the wet ingredients until just combined.
Step 5: Fold in the M&M's - Gently fold in the M&M's until evenly distributed throughout the dough.
Step 6: Scoop and Bake - Drop rounded balls of dough onto a prepared baking sheet, leaving space between each. Bake for 10-12 minutes until edges are lightly golden.
Step 7: Cool and Enjoy - Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack. Enjoy your cookies!
