Preheat the oven to 325 degrees F.
Grease an 8 1/2 by 4 1/2 by 3-inch loaf pan with 1 teaspoon of the butter and 1 teaspoon of flour, knocking out the excess. Sift the remaining cup of flour, baking powder, and salt into a bowl, and set aside.
Combine the remaining butter and the sugar in the bowl of a mixer and cream on high speed. Add the dry ingredients to the bowl, alternating with the eggs, beating on low speed, and scraping the sides of the bowl. Add the juice, zest, and vanilla, and beat until just incorporated.
Pour the batter into the prepared pan. Bake until the cake has risen, is golden brown on top, and a tester inserted into the center comes out clean, about 1 hour.
Remove the cake from the oven. Let rest in the pan for 10 minutes, then turn out onto a wire rack to cool for at least 30 minutes before serving.
Yield: 8 to 12 servings