Preheat oven to 375°F.

Line two sheet pans with parchment paper; set pans aside.

Using a large bowl, add flour, baking powder, baking soda and salt; stir until well combined; set bowl aside.

In a separate bowl, whisk together sour cream, milk, vanilla extract and lemon zest; set bowl aside.

Using a countertop mixer, cream together the butter and sugar until light and fluffy (~3-4 minutes on medium speed).

Add eggs; mix on low speed until well combined.

Add ½ of the flour mixture; mix on low speed until well combined.

Add ½ of the sour cream mixture; mix on low speed until well combined.

Repeat with the remaining flour and sour cream mixtures. (Note: Don’t forget to scrape the sides of the bowl with a spatula.)

Using an ice cream scoop (or a ¼-cup measure), drop ¼ cup scoops of batter onto the prepared baking pans. (Note: Leave 2” of space between scoops. I put 6 scoops on each pan.)

Let cookies cool on pans for 15 minutes and then transfer cookies to a cooling rack until completely cool.

Using a medium bowl, add confectioner’s sugar, corn syrup, vanilla extract and 5 Tbsp of hot water; whisk together until well combined. If needed, continue adding hot water 1 Tbsp at a time until the glaze is thick but spreadable. (Note: Err on the side of too thick rather than too thin!)

Flip each cookie over and use an offset spatula to spread glaze over half of the flat side. Place cookies back on cooling rack. (Note: You will have leftover glaze.)

Stir the melted chocolate into the remaining glaze. Add cocoa powder and stir until glaze is smooth. Add enough hot water (2-3 Tbsp) to create a thick, but spreadable glaze.

Using an offset spatula, spread the chocolate glaze evenly on the other half of the cookies.

Let glaze set for 1-2 hours before serving.