Sift flour, cocoa powder, baking powder and salt into a large bowl and whisk to blend evenly.
In a stand mixer fitted with the paddle attachment, beat butter and both sugars for 5 minutes, until very pale, creamy and fluffy. It should be almost white by the end of the mixing time. Beat in egg, espresso powder (if you're using it) and vanilla until well incorporated. Add flour mixture and mix on low speed until just combined.
Divide dough in half and wrap each well in plastic wrap, flattening it to form a disc. Refrigerate for about 45 minutes.
Remove one disc and unwrap it. Place the dough between two pieces of parchment paper and press down on it with a rolling pin along its length to soften it a bit. Continue rolling between the parchment (it will soften more as you roll) to ¼-inch thickness. Cut out shapes using the cutters of your choice. I get about 25 cookies if I use 2 to 3-inch wide heart cutters. Transfer cut-outs to parchment-lined baking trays, spacing them 2 inches apart. Refrigerate the trays with cut-outs for 15 minutes while your oven heats.
Preheat your oven to 325°F.
Bake cookie dough cut-outs for 10-12 minutes, until they feel dry but soft to the touch. Transfer trays to a wire rack to cool for 10 minutes before transferring cookies individually to the rack to finish cooling.
To make the filling, place chopped chocolate in a heatproof bowl. Add cream and honey to a saucepan and bring to a simmer over medium heat. When bubbles form around the edges, immediately pour the cream over the chocolate in the bowl. Swirl the bowl to cover all the chocolate with the cream and cover. Let stand for 1 minute, then stir gently from the center and working your way out to the sides until it transforms into a smooth glossy silky ganache. Let it cool for 15-20 minutes until thick and spreadable.
Spread about a teaspoon of ganache evenly over the undersides of half of the cookies and then gently press another cookie on top to make a sandwich. Let them set completely for about 1 hour then transfer to an airtight container for storage.