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1
Butter the sides only of a 10-inch springform pan.
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2
Preheat the oven to 350 degrees F.
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3
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.
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4
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.
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5
Add the spices to the remaining dry ingredients.
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6
Mix well.
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7
In a small bowl stir the egg and yogurt together to mix well.
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8
With a wooden spoon, stir the wet mixture into the dry mixture.
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9
Sprinkle the baking soda over the surface of the batter and gently but thoroughly stir it inches.
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10
Spread this batter over the mixture that was pressed into the bottom of the pan.
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11
With a rubber spatula smooth the top of the batter.
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12
Scatter the walnuts on top.
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13
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.
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14
Cool in the pan, on a rack, for 5 minutes.
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15
Then slide a knife around the edge of the cake to be sure it's not stuck.
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16
Remove the sides of the pan and cool cake completely.
