We like to use tart green apples with the peels left on.
Preheat the oven to 350°F. Grease and flour an 8-inch square baking pan and line the bottom with parchment paper.
Whisk together thoroughly in a large bowl, pinching out any lumps in the brown sugar:
Add and stir together until smooth:
Stir in:
Scrape the batter into the pan and spread evenly. Bake until a toothpick inserted into the center comes out clean, 40 to 45 minutes.
Let the cake cool in the pan on a rack. Serve warm, plain, or cool, unmold, and frost with: