Prepare the cookie dough. In a large bowl, beat the butter, sugar, and vanilla extract until creamy and well combined.
Add the egg and continue beating until fully mixed.
In the same bowl, add the flour, cocoa powder, salt, and baking powder. Mix with a spatula or spoon until you form a smooth and uniform dough.
Shape the dough into a rectangular block, wrap it in plastic wrap, and refrigerate for at least 3 hours, or overnight.
Preheat the oven to 350°F (180°C).
Remove the dough from the refrigerator and roll it out to about 1/4 inch thickness. Dust the work surface lightly with flour if needed.
Use a heart-shaped cookie cutter, or desired shape, to cut out the cookies.
Place the cookies on a baking sheet lined with parchment paper.
Chill the cookies in the refrigerator for 5 minutes to help them hold their shape while baking.
Bake the cookies in the preheated oven for 6-7 minutes.
Remove from the oven and let them cool completely on a wire rack.
Melt the chocolate (in a microwave in short intervals or using a double boiler). Decorate the cookies with the melted chocolate using a piping bag or spoon. Sprinkle Valentine's Day-themed sprinkles on top while the chocolate is still wet.
Keyword chocolate, cutout cookies, rolled cookies, sugar cookie, Valentine's Day