Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a mixing bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking powder, and salt. Set aside.
In another bowl, cream the unsalted butter and granulated white sugar together until light and fluffy, about 2-3 minutes.
Add the egg and pure vanilla extract, beating until well combined.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Melt the chopped bittersweet chocolate using a double boiler or microwave, then allow it to cool slightly.
Pour the melted chocolate into the dough, followed by the peppermint extract and additional salt. Stir until fully incorporated.
Drop rounded tablespoons of dough onto the prepared baking sheet, leaving space between each.
If desired, sprinkle the tops with colorful sprinkles or nonpareils.
Bake for 10-12 minutes until the edges are set. The centers may look slightly soft.
Let the wafers cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.
