In a large mixing bowl, add the softened butter, granulated sugar, light brown sugar, vanilla extract, kosher salt, and espresso powder. Beat with an electric mixer on medium speed until smooth and creamy.
¾ cup unsalted butter, ½ cup granulated sugar, ⅓ cup light brown sugar, 1 teaspoon vanilla extract, ½ teaspoon kosher salt, 1 tablespoon espresso powder
Mix in the egg and egg yolk until the mixture becomes light and fluffy.
1 large egg, 1 large egg yolk
Add the all-purpose flour and baking soda. Mix on low speed just until the dough is almost combined. Do not overmix to keep the cookies soft.
2 ¼ cups all-purpose flour, 1 teaspoon baking soda
Scoop about 2 tablespoons of dough for each cookie and place them on a parchment-lined baking sheet, leaving enough space for spreading.
Bake in a preheated oven at 350°F (180°C) for 10 to 12 minutes, or until the edges are lightly golden. The centers should remain soft. Allow the cookies to rest on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
In a large bowl, combine the heavy cream, espresso powder, vanilla extract, and powdered sugar. Beat with an electric mixer until stiff peaks form.
1 cup powdered sugar, 1 teaspoon vanilla extract, 2 tablespoons heavy cream, 1 teaspoon espresso powder
Gently fold in the room-temperature mascarpone cheese with a spatula until the mixture is smooth and creamy.
6.34 ounces mascarpone cheese
Transfer the mascarpone cream to a piping bag fitted with a round tip. Pipe the cream onto each cooled cookie.
Lightly dust the tops with cocoa powder before serving.
2 tablespoons cocoa powder