In a mixing bowl, whisk together the flour, baking powder, and salt. Set aside.
In the bowl of a stand mixer, cream together the butter and sugar. You can also do this with a handheld mixer or by hand.
Add the eggs and vanilla extract and blend until combined.
Add the dry ingredients and blend until a dough ball forms.
Remove half of the dough from the bowl and set aside.
In a double boiler, melt the chocolate. You could also do this in a small bowl in the microwave in 30-second increments.
Add the melted chocolate to the mixer bowl with the remaining half of the dough. Blend until combined.
Roll each of the doughs into a large rectangle. You will need extra flour for dusting the surfaces as you work.
Place one rectangle over the other. Then roll them into a log. If needed, you can use parchment paper on the outside to help roll them up.
Slice the log into thin cookie slices. Place on a baking sheet lined with parchment paper.
Bake at 375°F for 8-10 minutes. Remove to cooling rack once baked.