Step 1: Preheat your oven to 350°F (175°C) and line two large baking sheets with parchment paper or silicone baking mats.
Step 2: In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Set this dry mixture aside.
Step 3: In a large bowl or stand mixer, beat the softened but cool butter with granulated sugar and brown sugar for 1-2 minutes until the mixture is light and fluffy.
Step 4: Add the cold egg and the vanilla extract to the butter mixture. Beat until well combined, scraping down the sides of the bowl as needed.
Step 5: Gradually add the dry flour mixture to the wet ingredients while mixing on low speed. Mix until just combined; do not overmix.
Step 6: Gently fold in the Easter M&Ms and white chocolate chips by hand using a spatula.
Step 7: Scoop the dough into balls (about 2 tablespoons each). Roll the top of each dough ball in the pastel sprinkles.
Step 8: Place the dough balls on the prepared baking sheets, spaced 2 inches apart. Bake for 8 to 11 minutes.
Step 9: Remove from the oven when the edges are just set but the centers still look slightly soft. Allow the cookies to cool on the baking sheet for 5-10 minutes before transferring to a wire rack.