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

In a medium bowl, whisk together the flour and baking soda.

In a large bowl, cream together the softened butter, granulated sugar, brown sugar, and salt until the mixture is light and fluffy.

Add the vanilla extract, whole egg, and egg yolk, beating until fully incorporated.

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

Gently fold in the rainbow sprinkles and milk chocolate candies using a spatula.

Portion the dough into rounded tablespoons and place them 2 inches apart on the prepared baking sheets.

Bake for 10 to 12 minutes, or until the edges are set and lightly golden while the centers remain soft.

Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire cooling rack.