The 8-inch square pan yields the lightest-textured cake; the loaf is denser.
Have all ingredients at room temperature, about 70°F. Preheat the oven to 350°F. Grease and flour an 8-inch square baking pan or a 9 × 5-inch loaf pan.
Whisk together thoroughly in a medium bowl:
Beat in a large bowl, or in a stand mixer with the paddle attachment, until creamy, about 30 seconds:
Gradually add and beat on high speed until lightened in color and texture, 3 to 5 minutes:
Beat in:
On low speed, add the flour mixture in 3 parts, alternating with:
in 2 parts, beating after each addition just until incorporated and scraping the sides of the bowl with a silicone spatula as necessary. If desired, stir in:
Scrape the batter into the pan and spread evenly. Bake until a toothpick inserted into the center comes out clean, 25 to 30 minutes in a square pan, 1 hour to 1 hour 10 minutes in a loaf pan.
Let cool in the pan on a rack for 15 minutes, then invert onto the rack to cool completely.
Frost with:
or sprinkle with: