1. In a large bowl, mix brown sugar, granulated sugar, flour, nutmeg, and 2/3 cup butter.
2. Transfer 1 packed cup of the sugar mixture to a small bowl. Add nuts and cinnamon, mixing well.
3. To the mixture in the large bowl, add egg, buttermilk, baking powder, and baking soda; mix well. Pour batter into a buttered 9-inch cheesecake pan with removable rim. Sprinkle cinnamon-nut mixture evenly over batter.
4. Bake in a 350° oven until toothpick inserted in center comes out clean and cake begins to pull from pan sides, about 40 minutes (about 35 minutes in convection oven).
5. Cool on a rack at least 20 minutes. Remove pan rim. Serve warm or cool.