- 2 1/4 sticks unsalted butter
- 2 cups sifted cake flour (not self-rising; sift before measuring)
- 1 teaspoon baking powder
- 1/2 teaspoon salt
- 1/2 cup packed light brown sugar
- 1/2 cup granulated sugar
- 4 large eggs
- 1/2 teaspoon pure vanilla extract
- Preheat oven to 325°F 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 a dark chocolate brown. 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 2 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 into center comes out clean, 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.