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1
Preheat the oven to 350 degrees F. Butter an 8-inch-square baking pan.
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2
Line with parchment paper, leaving a 2-inch overhang on all sides.
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3
Lightly butter the paper.
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4
Prepare the streusel: Pulse the butter, sugar, peanuts, orange zest and vanilla in a food processor just until the nuts are coarsely chopped.
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5
Make the cake: Sift the flour, baking powder, baking soda and salt through a fine sieve into a large bowl.
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6
Beat the butter and sugar in a separate bowl with a mixer on medium-high speed until pale, about 5 minutes.
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7
Add the eggs, scrape down the sides of the bowl and beat on medium speed until fluffy, about 4 minutes.
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8
Reduce the speed to low.
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9
Add the flour mixture in 3 batches, alternating with the sour cream, beginning and ending with the flour mixture.
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10
Scrape down the bowl and finish mixing by hand (do not overmix).
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11
Pour half of the batter into the prepared pan and smooth the top.
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12
Sprinkle with half of the streusel and dollop with half of the jam.
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13
Spread the remaining batter on top.
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14
Sprinkle with the remaining streusel and top with the remaining jam.
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15
Bake until a toothpick inserted into the center of the cake comes out clean, 50 minutes to 1 hour.
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16
Transfer the pan to a rack and let the cake cool completely, then lift out the cake by the parchment paper and cut into squares.
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17
Photograph by Kana Okada
