Recipe excerpted from Modern Comfort Food by Ina Garten. Adding sour cream to the batter makes these cookies supremely moist and a bit cakelike.
Arrange two racks evenly spaced in oven. Preheat oven to 350°F. Line two sheet pans with parchment paper.
Put 10 tablespoons of the butter and the granulated sugar in the bowl of an electric mixer fitted with the paddle attachment and beat on medium-high 2 to 3 minutes, until light and fluffy. With mixer on low, add egg and 2 teaspoons of the vanilla extract and mix well, scraping down sides with a rubber spatula. Sift* flour, baking powder, baking soda, and salt into a bowl. With mixer on low, alternately add flour mixture and the sour cream in thirds and mix just until combined.
With a standard ice cream scoop (2 1/4-inches), place 5 level scoops of batter 2 inches apart on each prepared sheet pan. Bake 10 minutes, then rotate and switch the pans from top to bottom rack to bake cookies evenly. Bake another 6 to 8 minutes or until edges are lightly browned and a cake tester comes out clean. (Don't overbake them!) Cool on pans for 5 minutes, then transfer to a wire rack set over a sheet pan to cool completely.
For chocolate glaze: Place remaining 4 tablespoons butter, the chocolate, and coffee in a heatproof bowl and microwave on high 30 seconds. Stir mixture and continue to microwave in 30-second increments until chocolate is almost melted, allowing residual heat to finish melting chocolate completely. Stir mixture vigorously until smooth. Turn cookies so flat sides are up. Hold a cookie in your hand and, with a spoon, carefully pour chocolate glaze over half of the cookie, forming a line down the middle. Repeat for remaining cookies. Allow glaze to set 30 minutes.
For vanilla glaze: Whisk together confectioners' sugar, corn syrup, the remaining 1/2 teaspoon vanilla extract, and 2 tablespoons of the cream, adding the cream a few drops at a time until the glaze is smooth, thick, and barely pourable. Hold a cookie in your hand and, with a spoon, pour vanilla glaze over other half of the cookie right up to the chocolate glaze. You can smooth it out with an offset spatula if you need to. Repeat with remaining cookies. Allow glaze to set 30 minutes. Makes 10 cookies.
"Instead of using a sifter, I place dry ingredients in a coarse wire strainer set over a bowl and tap the side of the strainer with my hand," Ina says.