Preparation Put oven rack in middle position and preheat oven to 325°F. Butter a 15- by 10- by 1-inch baking pan, then line bottom with foil, leaving a 2-inch overhang on 2 ends, and butter foil. 3Whisk together flour, cinnamon, and salt in a bowl until combined. Beat together butter and sugar in a large bowl with an electric mixer at medium-high speed until pale and fluffy, about 3 minutes in a stand mixer (preferably fitted with paddle attachment) or 6 minutes with a handheld. Beat in yolk. Reduce speed to low, then mix in flour mixture until combined. Spread batter evenly in pan with an offset spatula. Lightly beat egg white in a small bowl, then brush some of it over batter and sprinkle evenly with pecans. Bake until top is golden brown and edges begin to pull away from sides of pan, 35 to 40 minutes. Cool in pan on a rack 10 minutes, then transfer with foil to a cutting board. Discard foil. Cut while still warm into 2-inch squares or, by halving squares diagonally, into triangles and cool completely on rack. Cooks' note:Cookies keep, layered between sheets of wax paper or parchment, in an airtight container at room temperature 2 weeks.
Preparation Put oven rack in middle position and preheat oven to 325°F. Butter a 15- by 10- by 1-inch baking pan, then line bottom with foil, leaving a 2-inch overhang on 2 ends, and butter foil. 3Whisk together flour, cinnamon, and salt in a bowl until combined. Beat together butter and sugar in a large bowl with an electric mixer at medium-high speed until pale and fluffy, about 3 minutes in a stand mixer (preferably fitted with paddle attachment) or 6 minutes with a handheld. Beat in yolk. Reduce speed to low, then mix in flour mixture until combined. Spread batter evenly in pan with an offset spatula. Lightly beat egg white in a small bowl, then brush some of it over batter and sprinkle evenly with pecans. Bake until top is golden brown and edges begin to pull away from sides of pan, 35 to 40 minutes. Cool in pan on a rack 10 minutes, then transfer with foil to a cutting board. Discard foil. Cut while still warm into 2-inch squares or, by halving squares diagonally, into triangles and cool completely on rack. Cooks' note:Cookies keep, layered between sheets of wax paper or parchment, in an airtight container at room temperature 2 weeks.