• In a medium bowl, sift together the flour, cocoa, and baking powder and set aside. (Alternately, you can use 280g of self-raising flour in this recipe, and leave out the baking powder and salt).
• In a small cup combine the milk and instant espresso; set aside. Using a hand mixer or stand mixer with a paddle attachment in a large bowl, cream the butter, sugar, pure vanilla extract, zest, and salt on high speed until creamy, about 3 minutes. Switch mixer to medium speed and add the eggs, one at a time and beat until combined. Beat in the espresso mixture.
• Scrape down the sides and the bottom of the bowl as needed. Fold in the dry ingredients until just incorporated. Cover tightly and chill the cookie dough for at least 1 hour and up to 3 days.
• Position racks in the upper and lower thirds of the oven and preheat to 350°F. Line two baking sheets with parchment paper; set aside. Once firm, roll the dough into 1-inch balls and arrange ½ inch apart on the prepared baking sheets; chill the cookies for at least 15 to 30 minutes in the freezer.
• Bake chocolate thumbprint cookies for 6 minutes, remove them from the oven and use your thumb to press a slight indentation into the center of each cookie. Fill each indentation with about a teaspoon of Dulce de leche and return to the oven. Continue baking until cookies are golden brown, about 10 to 24 minutes longer.
• Allow the cookies to cool on the baking sheets for 5 minutes, then remove to a wire rack to cool completely before glazing. Store the Chocolate Thumbprint Cookies in an airtight container at room temperature for up to 3 days or in the refrigerator for up to a week.

How to Make Vanilla Glaze

• Whisk the glaze ingredients together until smooth. Add more liquid to thin out or add more confectioners’ sugar to thicken to your desired consistency. Drizzle over-cooled the Chocolate Thumbprint Cookies. Enjoy!