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1
Heat oven to 350 degrees.
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2
Grease a 9-inch round cake pan.
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3
In a small saucepan over medium heat, melt 3 tablespoons (45 grams) butter.
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4
Add the brown sugar and lemon juice; stir until sugar melts, about 3 minutes.
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5
Scrape mixture into bottom of prepared pan.
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6
Grate 1/2 teaspoon zest from one of the oranges, then slice off the tops and bottoms of both oranges.
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7
Place oranges on a clean, flat surface, and slice away the rind and pith, top to bottom, following the curve of the fruit.
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8
Slice each orange crosswise into 1/4-inch-thick wheels; discard any seeds.
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9
Arrange orange wheels on top of brown sugar mixture in a single, tight layer.
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10
In a large bowl, whisk together orange zest, cornmeal, flour, baking powder and salt.
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11
In a separate bowl, cream together remaining 2 sticks (225 grams) butter with granulated sugar.
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12
Beat in eggs, one a time, then beat in sour cream and vanilla.
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13
Fold in the dry mixture by hand.
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14
Scrape batter into pan over oranges.
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15
Transfer to oven and bake until cake is golden brown and a toothpick inserted in the center emerges clean, 40 to 50 minutes.
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16
Cool cake in pan 10 minutes, then run a knife along pans edges to loosen it; invert onto a platter and cool completely before serving.
