1 cup (2 sticks) unsalted butter, at room temperature
1 cup firmly packed light brown sugar
1 large egg yolk
1 teaspoon vanilla extract
1/4 teaspoon salt
2 cups all-purpose flour
7 to 8 ounces milk chocolate, broken into pieces, or 1 1/2 cups milk chocolate chips
1 cup chopped almonds, toasted
1. Preheat the oven to 350°F. Line a 9-by-13-inch baking pan with parchment.
2. Prepare the crust. In a large bowl, with an electric mixer, beat together the butter and sugar on medium speed until light, about 2 minutes. Beat in the egg yolk, vanilla, and salt. On low speed, gradually beat in the flour just until mixed. The dough will be stiff. Pat the dough evenly over the bottom of the baking pan.
3. Bake in the center of the oven until pale gold on top, about 20 minutes.
4. Remove the pan from the oven and scatter the chocolate pieces evenly over the crust. Return the pan to the oven for 1 minute. Remove the pan again and, using a knife, spread the chocolate evenly over the crust. Sprinkle evenly with the almonds.
5. Let cool completely in the pan on a wire rack. Using a sharp knife, cut into small squares, then carefully remove from the pan with a small offset spatula or an icing spatula.