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1
Make the caramel: Combine the sugar, 1/3 cup water and the kosher salt in a medium saucepan over medium heat, stirring just until the sugar dissolves.
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2
Cook, gently swirling the pan occasionally but not stirring, until amber, 8 to 10 minutes.
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3
Brush any sugar crystals off the side of the pan with a wet pastry brush.
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4
Remove from the heat and carefully whisk in the butter (the mixture will bubble).
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5
Pour into a 9-inch-round cake pan, tilting the pan to coat the bottom; set aside.
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6
Slice off the top and bottom of the oranges.
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7
Place the oranges cut-side down and cut off the peel and white pith with a chef's knife, following the curve of the fruit.
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8
Cut along both sides of each membrane to remove the segments.
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9
Set the segments aside, discarding any seeds.
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10
Make the cake: Preheat the oven to 350 degrees F. Spread the almonds on a baking sheet and roast until golden brown, 8 to 10 minutes.
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11
Let cool, then transfer to a food processor and pulse until finely ground.
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12
Transfer to a medium bowl; add the flour, baking powder, baking soda and kosher salt and whisk to combine.
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13
Beat the butter and sugar in a large bowl with a mixer on medium-high speed until fluffy, about 5 minutes.
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14
Beat in the eggs one at a time, scraping down the bowl as needed.
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15
Beat in the orange zest.
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16
Reduce the mixer speed to low; beat in the flour mixture in 3 batches, alternating with the sour cream, beginning and ending with flour, until just smooth.
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17
Arrange the orange segments in the cake pan in concentric circles.
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18
Add the batter and smooth the top.
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19
Bake until golden brown and a toothpick inserted into the center comes out clean, 40 to 45 minutes.
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20
(Tent with foil if the top gets too dark.)
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21
Transfer to a rack and let cool slightly, then run a knife around the edge of the cake and invert onto a platter.
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22
Let cool completely.
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23
Sprinkle with sea salt.
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24
Photograph by Kana Okada
