A moist, warmly spiced old‑fashioned oatmeal cake, perfect for breakfast or dessert, featuring oats, cinnamon, and optional nuts or raisins.

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Preheat oven to 350 °F (175 °C). Grease and flour an 8‑ or 9‑inch square cake pan.
In a bowl, combine oats and buttermilk; let sit 10 minutes to soften oats.
In a large bowl, cream butter with granulated and brown sugars until light and fluffy, about 2–3 minutes.
Add eggs one at a time, beating well after each, then mix in vanilla extract.
In a separate bowl, whisk together flour, baking powder, baking soda, cinnamon, nutmeg (if using), and salt.
Alternate adding dry ingredients and oat mixture to butter mixture, beginning and ending with dry ingredients. Stir until just combined. Fold in nuts or raisins, if using.
Spread batter evenly in prepared pan. Bake 25–30 minutes, or until a toothpick inserted in center comes out clean.
Cool cake in pan on a wire rack for about 10 minutes, then remove and cool completely or serve warm.

Substitute a 9‑inch round pan if preferred; adjust baking time slightly as needed.
Serve warm with a dusting of powdered sugar or a cream cheese glaze.
Leftovers keep well, covered, for 3–4 days at room temperature or frozen slices up to 2 months.
For a richer texture, use quick oats instead of rolled oats.