Preheat oven to 350 degrees F. Line a baking sheet with parchment paper and set aside.
Add butter, powdered sugar and granulated sugar to the bowl of a mixer. Mix on medium speed until creamy.
Add vanilla extract and egg to the bowl. Mix on medium speed for 1-2 minutes until combined.
Add salt, baking powder, and flour a mixing bowl. Mix on low speed for 1 minute and then change setting to medium speed for an additional 2 minutes.
Moisten your hands with cold water and roll the dough into 1” balls, placing them on prepared baking sheet - 2 inches apart. If dough begins to stick to hands while working, simply wet them again under cold water and start again. Bake for 8-10 minutes or until cookies are a light golden color.
Remove cookies from oven and use your thumb to gently press the center of each cookie to create a well for the filling. Allow cookies to cool on the baking sheet for 2 minutes before transferring to a wire rack to cool completely.
For the filling, melt the white chocolate in the microwave on 50% power for up to 30 seconds. Stir and continue melting at 50% power for an additional 15 seconds, repeating this process until completely melted.
Divide the white chocolate into separate bowls and add 1-2 drops of food coloring, stirring well to incorporate. If the white chocolate seizes up after food coloring is added, simply add a drop or two of cooking oil and stir. If this doesn’t fix the problem, microwave again on 50% power for a few seconds and stir again and the chocolate should smooth out.
Spoon colored chocolate into the well of each cookie, adding sprinkles immediately if desired.
Allow chocolate to cool and harden before serving.