Instructions: 1. Preheat the oven to 375 degrees. Coat an 8-inch square baking pan with nonstick oil spray. Melt butter in a medium saucepan or in a mixing bowl in a microwave oven. Stir in the flour, brown sugar, and nutmeg until the mixture resembles coarse crumbs. Measure out and reserve 1/2 cup of the crumbs.

2. In a small bowl, whisk the baking soda into the buttermilk or yogurt then whisk in the vanilla and egg yolk. Stir the liquid ingredients into the dry ingredients. Spread the batter evenly in the pan, then sprinkle with the reserved 1/2 cup crumbs.

3. Bake until golden brown and a toothpick inserted into the center comes out clean, about 25 minutes. Serve warm or at room temperature on the day of baking. (The cake may be covered and frozen for up to 1 month.)

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