In a medium bowl, mix softened butter and sugar until smooth. Add the egg and stir well to combine. Sift in the flour and fold until fully incorporated.
Cover the dough with plastic and rest in a fridge for at least 30 minutes.
Preheat the oven to 350˚F (180˚C).
Sprinkle flour on the work surface and rolling pin so the dough won’t stick. Roll out the dough to ¼- to ⅛-inch (6- to 3-mm) thickness. Using a 3-inch (7-cm) round cookie cutter, cut out the dough.
Cut out center of each cookie with using a 2-inch (5-cm) round cookie cutter.
Place the cookie on a parchment-lined baking sheet and bake for 10 minutes.
Take out the sheet from the oven and place hard candies in the center of each cookies. Bake for 3-5 minutes or until the hard candy melts and spreads out.
Let the cookies cool completely.
In a microwave-safe bowl, melt the white chocolate, about 10-15 seconds.
For the bottom cookies, add your favorite sprinkles onto the hard candy. Take the top cookies and drizzle melted chocolate around the rims. Immediately sandwich the 2 cookies and set in fridge for 15 minutes.