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1
Preheat the oven to 375u00b0 F.
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2
Butter a springform pan and line the bottom with a circle of parchment paper.
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3
Mix together the walnuts, the cinnamon, and 2 tablespoons of the sugar in a bowl and set aside.
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4
In the bowl of a stand mixer (or using hand beaters), beat together the butter and 1 1/2 cups sugar until light-colored and fluffy.
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5
Add the eggs and the vanilla and beat until combined.
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6
Sift the dry ingredients together (you will have sifted the flour twice, which keeps the cake light even with the addition of the sour cream).
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7
With the mixer running at low speed, alternate adding the dry ingredients and the sour cream to the butter and sugar mixture. You want 3 additions of each, ending with the sour cream. Be sure not to over-mix!
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8
Use a wooden spoon or a spatula to fold in the chocolate chips.
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9
Pour half of the batter into the prepared springform pan.
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10
Starting on the outside edge, place the apple slices in a concentric circle. Sprinkle half of the cinnamon-sugar-walnut mixture over the apples, then pour in the rest of the batter.
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11
Smooth with a rubber spatula.
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12
Top the cake with the remainder of the cinnamon-sugar-walnut mixture, then bake it for 40 minutes, or until it's golden-brown and a toothpick inserted in the center comes out clean.
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13
Let the cake cool in the pan until the edges start to pull away from the sides.
