Preheat oven to 200 degree Celsius. Line baking sheet with parchment paper and keep aside.
In a bowl, sieve flour, baking powder, cocoa powder, salt together. Keep aside.
In a big bowl, mix softened butter and sugar using a hand mixer. Beat for a minute or two until light and airy. Add the egg and vanilla, and beat for 30 seconds more.
Flour the work area and with the help of a rolling pin, roll the dough to 1/4 inch thickness. Use flour generously for dusting if required. Use cookie cutters to cut cookies and place on the baking sheet. Gather the leftover dough, reroll and repeat to cut more cookies.
Bake for 7-8 minutes. Allow them to cool before transferring to wire rack to cool completely.
In a double boiler, melt chocolate . Dip half the cookie in the chocolate and instantly shower sprinkles on the cookie. Wait for the chocolate to dry up before serving.