Preheat your oven to 350°F (175°C). While the oven heats up, line two baking sheets with parchment paper to prevent sticking.
In a medium mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, and fine sea salt until well combined. Set this dry mixture aside for later use.
In a large mixing bowl, use an electric mixer to cream the softened butter and granulated sugar together. Mix on medium speed for about 3 minutes until the mixture is light, fluffy, and pale in color.
Beat in the large egg and pure vanilla extract into the creamed mixture. Continue mixing on low speed until fully incorporated.
Gradually introduce the dry flour mixture to the wet ingredients. Mix on low speed just until the flour is absorbed—do not overmix to maintain a tender cookie texture.
Using a cookie scoop or tablespoon, portion out the dough and roll each scoop into a ball. Place them on the lined baking sheets, ensuring to leave about 2 inches of space between each cookie for spreading during baking.
Gently flatten each dough ball slightly using the palm of your hand, creating a disc shape. Bake in the preheated oven for 10-12 minutes, watching for the edges to turn golden while the centers remain soft to the touch.
After baking, remove the cookies from the oven and allow them to cool on the baking sheet for 5 minutes. After cooling, transfer them to a wire rack to cool completely.
Once the cookies have cooled down entirely, take one cookie and spread a generous layer of vanilla frosting on the bottom side. Top it with another cookie to create a delightful sandwich.
For a colorful finish, gently roll the edges of each sandwich cookie in rainbow sprinkles, adding a joyful touch to your creation!
Notes
Perfect for sharing or enjoying with a glass of milk.