01 - Preheat oven to 350°F. Line two baking sheets with parchment paper and set aside.
02 - In a medium bowl, whisk together the all-purpose flour, baking powder, and salt until evenly distributed.
03 - In a large bowl, beat the softened unsalted butter, granulated sugar, and light brown sugar using an electric mixer on medium speed until the mixture is light and creamy, about 2 to 3 minutes. Add the egg and vanilla extract, then mix until fully incorporated.
04 - Gradually add the dry ingredient mixture to the creamed butter mixture, mixing on low speed just until the dough comes together. Be careful not to overmix.
05 - Scoop 1 tablespoon of dough and flatten it slightly in the palm of your hand. Place ½ teaspoon of strawberry jam in the center, then cover with another tablespoon of dough. Pinch the edges together tightly to seal completely and gently roll into a smooth ball. Repeat with the remaining dough and jam.
06 - Place the filled cookie dough balls onto the prepared baking sheets, spacing them about 2 inches apart to allow for spreading.
07 - Bake for 12 minutes or until the edges are lightly golden. Allow the cookies to rest on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
08 - In a small bowl, whisk together the powdered sugar, milk, vanilla extract, and a drop of food coloring if desired, until smooth and slightly thickened. Spread the glaze over the cooled cookies and decorate with rainbow sprinkles. Let the glaze set before serving.