Sift flour, baking powder, and salt into a medium bowl. Set aside.
In a stand mixer fitted with the paddle attachment, cream butter and sugar until light and fluffy, about 3 minutes.
Add egg yolk and orange zest and mix until combined.
Add dry ingredients and mix until combined, but don’t overmix.
Roll out dough on a lightly floured surface into a log that’s about 2 inches in diameter
Wrap the dough log tightly in plastic wrap and refrigerate for at least an hour.
When you’re ready to bake the cookies, preheat the oven to 325˚F and line 2 baking sheets with parchment paper.
Slice the dough log into 1/4-inch thick rounds and place on prepared baking sheets at least 1-inch apart. Bake about 15 minutes or until golden brown on the bottom and edges. Remove from oven and let cool completely on cooling racks.
Put 8 ounces of the chocolate into a microwave safe bowl and set aside the remaining 4 ounces.
Microwave the 8 ounces of chocolate in 20 second increments on 50% power, stirring well between each interval, until the chocolate is almost melted. It’s important not to over-heat the chocolate. There should still be small lumps. It usually takes 3 intervals of 20 seconds at 50% power, followed by stirring, to get it to this point.
Once almost melted, add the remaining 4 ounces of chocolate and stir until all the chocolate is melted and smooth. The chocolate should feel slightly cool to the touch.
Line a tray with clean parchment. Dip half of each cookie in the chocolate and shake off the excess, being careful not to get crumbs in the chocolate. Allow to sit at room temperature until the chocolate is set.
