Step 1

Preheat oven to 325 degrees. Butter two 9-by-5-inch loaf pans; dust with flour, tapping out excess. In a bowl, whisk together flour and salt. (If making the lighter version, add baking powder at same time as salt.)

Step 2

With an electric mixer on high speed, beat butter and sugar until pale and fluffy, about 8 minutes. Scrape down sides of bowl. Reduce speed to medium; beat in vanilla. Add eggs, one at a time, beating thoroughly after each and scraping down sides of bowl. Reduce speed to low; add flour mixture in 2 batches (alternating with sour cream if making the lighter version), beating until just incorporated.

Step 3

Divide batter evenly between prepared pans. Tap pans on counter; smooth tops with an offset spatula. Bake until a cake tester inserted into center of each cake comes out clean, about 70-75 minutes. Transfer pans to a wire rack to cool 30 minutes. Turn out cakes onto rack to cool completely.