Preheat oven to 350°F (175°C) and line two large baking sheets with parchment paper or silicone mats.

In a large bowl or stand mixer, cream together the softened butter, granulated sugar, and brown sugar on medium-high speed until light and fluffy, approximately 3 minutes.

Add the eggs one at a time, beating well after each addition, then stir in the vanilla extract.

In a separate bowl, whisk together the all-purpose flour, baking soda, and salt to ensure even distribution of leavening agents.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined.

Fold in 1 cup of the pastel M&Ms and all of the white chocolate chips by hand using a spatula.

Scoop rounded tablespoons of dough and place them on the prepared baking sheets, ensuring 2 inches of space between each cookie.

Press the remaining 0.5 cup of M&Ms into the tops of the dough balls to ensure they are visible after baking.

Bake for 9 to 11 minutes, or until the edges are set and just barely golden; do not overbake as the center should remain soft.

Let the cookies rest on the baking sheet for 5 minutes to firm up before transferring them to a wire cooling rack.