Laurie Colwin's famous nutmeg cake. The technique is a little different. This is a rich cake top over a cookie base. If you don't know Laurie check this out.
Butter the sides only of a 10-inch springform pan.
Preheat the oven to 350 degrees F.
In a large mixing bowl, combine the butter, cut into 6-8 pieces, with the flour and dark brown sugar. Using a pastry blender, cut the butter into the flour and sugar until the mixture resembles fine meal.
Measure out 2 1/2 cups of this mixture and spread it evenly in the bottom of the prepared pan. With your hand flat, firmly compress the mixture evenly into the bottom of the pan.
Add the spices to the remaining dry ingredients.
In a small bowl stir the egg and yogurt together to mix well.
With a wooden spoon, stir the wet mixture into the dry mixture.
Sprinkle the baking soda over the surface of the batter and gently but thoroughly stir it inches.
Spread this batter over the mixture that was pressed into the bottom of the pan.
With a rubber spatula smooth the top of the batter.
Scatter the walnuts on top.
Bake in a preheated 350 oven for 50-55 minutes or until a toothpick comes out clean and the sides of the cake have shrunk slightly away from the pan.
Cool in the pan, on a rack, for 5 minutes.
Then slide a knife around the edge of the cake to be sure it's not stuck.
Remove the sides of the pan and cool cake completely.