Cream 1 cup of softened unsalted butter and 1 cup of granulated sugar in a large bowl for about 3 minutes until light and fluffy. Add 1 large egg and 1 teaspoon of pure vanilla extract, mixing until well combined. In another bowl, whisk together 2 cups of all-purpose flour, ⅓ cup of Dutch process cocoa powder, 1 teaspoon of baking powder, and ½ teaspoon of salt. Gradually incorporate the dry ingredients into the creamed mixture.

Divide the dough into two equal parts, shape each into a disc, wrap in plastic wrap, and refrigerate for at least 1 hour.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. Roll out one disc of chilled dough on a floured surface to about 1/8 to 1/4 inch thick, and cut out shapes using a heart-shaped cookie cutter.

Bake the cut-out cookies for 9 to 10 minutes, until edges feel crispy and firm. Allow cookies to cool on a wire rack.

Beat together ½ cup of softened butter, ¼ cup of half and half (or milk), 1 teaspoon of vanilla extract, and a pinch of salt in a medium bowl. Gradually add in 2 cups of powdered sugar, mixing until smooth.

Pipe a generous amount of the filling onto the center of half the cooled cookies, then place the remaining cookies on top to create sandwiches.