Step 2

Whisk together flour, baking powder, and kosher salt in a bowl. Beat butter and confectioners’ sugar with an electric mixer on medium speed until light and fluffy, 1 to 2 minutes. Beat in vanilla. Decrease mixer speed to low and gradually beat in flour mixture until combined. Finely chop 4 oz. chocolate; stir into dough.

Step 4

Divide dough in half; shape each into a 7 1/2-inch-long, 13/4-wide log. Cover logs with plastic wrap and chill at least 4 hours or up to overnight.

Step 6

Preheat oven to 350°F. Line baking sheets with parchment paper. Slice each log into 1/4-inch-thick cookies and place 1-inch apart on prepared baking sheets. Bake until edges are lightly golden, 12 to 15 minutes. Transfer cookies to a wire rack to cool.

Step 8

Line a baking sheet with parchment paper. Microwave remaining 8 ounces chocolate in a bowl 30 seconds; stir. Continue to microwave and stir in 10-second intervals until melted. Dip half of each cookie into melted chocolate and place on prepared baking sheet. Sprinkle lightly with sea salt. Refrigerate until chocolate is set, 10 to 15 minutes. Fruit-and-Nut Slice-and-Bake Cookies: Omit chocolate and sea salt and stir in 1/2 cup each chopped toasted nuts and dried fruit at end of step

Step 10

Lemon Slice-and-Bake Cookies: Omit chocolate and sea salt and stir in 1 1/2 Tbsp. lemon zest at end of step

Step 11

Roll dough into logs, and roll logs in 1/2 cup yellow sanding sugar before slicing, coating edges.