Makes 16 cookies
1 3/4 cups all-purpose flour
3/4 teaspoon baking soda
1 stick unsalted butter, at room temperature
6 tablespoons packed dark brown sugar
6 tablespoons granulated sugar
1 extra-large egg, at room temperature
2 tablespoons Diet Pepsi, at room temperature
1 teaspoon vanilla bean paste or pure vanilla extract
6 ounces bittersweet chocolate, cut into ½ inch chunks
1 teaspoon Maldon salt or coarse sea salt
Sift the flour and baking soda. Set aside.
Using an electric mixer fitted with the paddle attachment and beat the butter on medium speed for about 3 minutes until soft and smooth. Add the brown sugar, granulated sugar and beat on medium-high speed for 5 minutes until light and fluffy. Scrape down the sides of the bowl. Add the egg, Diet Pepsi and vanilla and beat for 1 to 2 minutes until just blended. Add the flour mixture and beat on low speed until just combined. Using a rubber spatula, scrape down the sides of the bowl. Stir until just blended.
Using a 3 tablespoon ice cream scoop, shape the dough into balls and arrange them close together on a large plate or small baking sheet. Cover and refrigerate for at least 1 hour until well chilled.
Preheat the oven to 350°F. Line 2 baking sheets with non-stick liners. Arrange the chilled dough on the prepared baking sheets about 2 inches apart. Using the palm of your hand, flatten each dough mound slightly. Lightly sprinkle with salt.
Bake for 12 minutes, switching the baking sheets positions halfway through baking, until light golden brown. Let cool completely.