Cake
Topping
For the cake Adjust oven rack to middle position and heat oven to 375 degrees. Grease and flour 13 by 9-inch baking dish. Process flour, sugar, cinnamon, nutmeg, baking soda, and salt in food processor until combined, about 3 seconds. Add butter and pulse until mixture resembles wet sand, about 8 pulses. Transfer to large bowl.
For the topping Return ½ cup cake mixture to now-empty processor. Add sugar and butter and pulse until mixture resembles wet sand, about 4 pulses.
Whisk buttermilk and eggs into remaining cake mixture until smooth. Pour into prepared dish and sprinkle with topping. Bake until toothpick inserted in center comes out clean, 25 to 30 minutes. Let cake cool in dish
on wire rack for at least 30 minutes. Slice and serve.