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1
Preheat oven to 350u00b0F.
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2
Generously butter bundt pan and dust with flour, knocking out excess.
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3
Whisk together flour, baking soda, salt, and baking powder in a bowl.
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4
Pulse walnuts, cinnamon, 1/4 cup sugar, and a pinch of salt in a food processor until nuts are chopped.
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5
Add melted butter and pulse once to combine.
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6
Beat together remaining 1 1/2 sticks butter and remaining cup sugar in a large bowl with an electric mixer at high speed until pale and fluffy, about 3 minutes in a standing mixer or 5 minutes with a handheld.
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7
Reduce speed to medium and add eggs 1 at a time, beating well after each addition, then beat in sour cream and vanilla until smooth and fluffy, about 2 minutes more in a standing mixer or 4 minutes more with a handheld.
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8
Reduce speed to low and add flour mixture, scraping down side of bowl occasionally and mixing until just combined.
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9
Sprinkle half of nut mixture evenly in bottom of bundt pan.
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10
Spoon half of batter over nuts and smooth with a rubber spatula.
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11
Sprinkle batter in pan with remaining nut mixture and top with remaining batter, smoothing top.
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12
Bake in middle of oven until cake begins to pull away from side of pan and a tester comes out clean, 45 to 50 minutes.
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13
Cool cake in pan on a rack 1 hour, then run a thin knife around outer and inner edges.
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14
Place rack on top of pan, then flip to invert cake onto rack.
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15
Cool completely.
