Makes 1 (8 -1/2 by 4-1/2 inch) loaf.
Active time: 25 minutes. Start to finish: 3-1/2 hours. (including cooling)
(I bet this would go well with the above chocolate sauce, if you simply can’t go one dessert with out chocolate.)
2-1/4 sticks unsalted butter
2 cups sifted cake flour (not self-rising; sift before measuring-if using all-purpose flour instead, for every cup of cake flour, sub in one cake of all-purpose flour minus 2 Tbsp.)
1 tsp. baking powder
1/2 tsp. salt
1/2 cup packed brown sugar
1/2 cup granulated sugar
4 large eggs
1/2 tsp. pure vanilla extract
Preheat oven to 325ºF with rack in middle. Butter and lightly flour an 8 -1/2 by 4-1/2 inch loaf pan.
Heat butter in a 10-inch heavy skillet over medium heat until milk solids on bottom are dark chocolate brown. (It should smell nutty.)
Transfer to a shallow bowl and chill in freezer until just congealed, about 15 minutes.
Whisk together flour, baking powder and salt.
Beat together brown butter and sugars with an electric mixer until fluffy, about two minutes. Add eggs 1 at a time, beating well after each addition. Beat in vanilla. At low speed, mix in flour mixture until just incorporated.
Transfer batter to pan, smoothing top, then rap pan on counter to settle batter. Bake until golden brown and a wooden pick inserted in the center comes out clean, about 1 to 1-1/4 hours. Cool in pan 30 minutes, then invert cake onto a rack and cool completely, right side up, 1 hour.