Gently stir in the dry ingredients until just combined.
Add the melted butter and gently mix until all the butter is incorporated.
Spoon the batter evenly into the prepared mini muffin pan using a small cookie scoop or teaspoon. Add toppings if using.
Bake for 10-12 minutes or until golden brown and crispy around the edges. Let cool in the pan for 5 minutes, then transfer the financiers to a wire rack to cool completely. Dust with powdered sugar before serving if desired.
Notes
Leftovers can be stored in an airtight container for up to 3 days at room temperature.