Preheat oven to 350 F. Line cookie sheets with silicone baking mat or parchment paper.
Beat butter together with ½ cup granulated sugar and brown sugar until well-combined.
Scrape down sides of the bowl, and mix in egg until incorporated.
Mix in melted chocolate and vanilla extract.
Add cocoa powder, baking powder, and salt. Mix in until combined.
Mix in flour until just combined.
Scoop dough by level tablespoons and roll into a ball.
Roll dough in remaining ¼ cup granulated sugar.
Place 2-inches apart on prepared baking sheets.
Bake for 8-11 minutes.
Remove from oven, and immediately press an unwrapped kiss into the top of each cookie.
Once cookies have a kiss, remove cookies to cooling rack to finish cooling.
Butter: I use salted butter in these cookies.
Cool room temperature: Cool room temperature butter should be about 68-70F. The butter should dent when pressed, but the stick of butter shouldn't be too warm or smooshy.
Semi-sweet chocolate: I recommend using semisweet baking chocolate because it melts better. Chocolate chips can have additives that can make it more difficult to get smooth melted chocolate.
Cocoa powder: I use regular unsweetened cocoa powder in this recipe. I haven't tried using Dutch-processed cocoa powder in these cookies.
Flour: It's important to properly measure the flour by either weighing it or by sifting or stirring the flour to break it up, lightly spooning it into the measuring cup, and then leveling it. This helps to avoid getting too much flour in your cookie dough. Too much flour can make the dough crumbly.