Makes 1 9x5-inch pan
Cuts into 12 to 16 slices
1 cup unsalted butter at room temperature
1 cup sugar
4 eggs at room temperature
2 tsp vanilla extract
2 cups all-purpose flour
1 1/4 tsp baking powder
1/4 tsp salt
2/3 cup sour cream (full-fat)
4 oz bittersweet chocolate, chopped
1. Preheat the oven to 325°F. Grease a 9-x-5-inch loaf pan and dust it with flour, tapping out any excess.
2. Beat the butter and sugar until fluffy, about 2 minutes, using electric beaters or in a stand mixer fitted with the paddle attachment. Add the eggs one at a time, beating well after each addition. Stir in the vanilla.
3. In a separate bowl, sift the flour, baking powder and salt. Add this alternately with the sour cream and blending well after each addition, starting and finishing with the flour. Scrape half of this batter into another bowl.
4. Melt the chocolate by stirring it in a bowl placed over a pot of barely simmering water. Add the warm chocolate to one of the bowls of batter and stir until blended. Dollop vanilla batter and chocolate batter in alternating spoonfuls into the pan. Use a paring knife to swirl the batter. Bake the cake for 60 to 70 minutes, until a tester inserted in the centre of the cake comes out clean. Cool the cake for 30 minutes in the pan, then turn it out to cool completely.
5. The cake will keep up to 5 days stored at room temperature in an airtight container.
NOTE: Loaf pans seem to have the greatest variation in size. While an 8-inch square pan is 8-inches, and a 9-inch pie plate is 9-inches, loaf pans can be 8 ¾-x-5 ¼ inches or 9 1/8-x-4 ¾ inches or many other combinations. You can use pans slightly larger or smaller, but the bake time may have to be adjusted slightly – a loaf in a shorter but taller pan could take longer than one in a wider, longer pan. Unless your pan is more than ½-inch shorter in width, length AND height you shouldn’t run into an issue with the batter spilling over as it rises.