Preheat your oven to 375°F, then line a baking pan with parchment paper. Remember, we'll lower the temperature to 350°F once the cookies are in.

Melt the chocolate and butter in a microwave-safe bowl in short bursts, stirring until smooth. Let it cool slightly.

Whisk the egg and sugar in a medium bowl until pale and thick. Stir in the cooled chocolate mixture.

Mix cornstarch, cocoa powder, baking powder, and salt in a small bowl. Fold this into the chocolate mixture. Add chocolate chips if you like.

Rest the dough for 10-15 minutes to thicken. If your kitchen is warm, chill it in the fridge for 5-8 minutes.

Scoop 1 ½ tablespoons of dough onto the baking sheet, spacing them 2 inches apart.

Bake at 350°F for 8-10 minutes until the tops are shiny and crackled. Let them cool on the tray before transferring to a rack.