Preheat oven to 350 and line 2 baking sheets with parchment paper.

In a medium bowl, whisk together the flour, baking powder and salt.

In a stand mixer beat together the softened butter and sugar at medium speed until light and fluffy.

Add whole egg and egg yolk, milk, vanilla and lemon extract if using. Beat until combined. Batter may appear lumpy but it will even out. Add the flour mixture slowly on low speed, beating briefly after each addition, scraping down the bowl as necessary to form a soft batter.

Drop rounded tablespoons onto the prepared baking sheets and place one sheet in the oven at a time, rotating the sheet halfway through the cooking time. Bake until light golden around the edges but pale on top. Remove carefully from sheet and place on a wire baking rack to cool.

Make Icing:

In a large measuring cup, combine the powdered sugar, milk and vanilla extract. Stir until a thick icing forms, adding more milk as needed to make the icing spreadable.

Transfer half of the vanilla icing to a small bowl and add the cocoa and coffee granules and stir to combine. If necessary add more milk to achieve the right coonsistency.

Turn cookie over so the flat side is up. Frost half of the cookie using a small offset spatula or butter knife with the vanilla icing. Then go back and do the other half with the black icing. Let dry and store in an airtight container with wax paper between each layer.