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1
Make Orange Caramel Layer:
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Preheat oven to 350 with rack in middle. Lightly butter a 9-inch round cake pan, then line bottom with a round of parchment paper, and side with a strip of parchment.
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3
Bring sugar and water to a boil in a small heavy saucepan over medium heat, stirring until sugar has dissolved, then wash down any sugar crystals from side of pan with a pastry brush dipped in cold water. Boil, without stirring, swirling pan occasionally so caramel colors evenly, until dark amber.
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4
Remove from heat and add butter, swirling pan until incorporated, then carefully but quickly pour caramel into cake pan, tilting pan to coat evenly.
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5
Grate zest from oranges and reserve for cake. Cut remaining peel, including white pith, from both oranges with a paring knife. Cut oranges crosswise into 1/4-inch-thick slices. Remove any seeds and arrange slices in 1 layer over caramel.
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6
Make Cake:
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Beat butter with sugar using a electric mixer until just combined. Add eggs 1 at a time, beating well after each addition. Mix in orange-flower-water and reserved zest.
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8
Whisk together flour, baking powder, and salt. With mixer at low speed, mix almonds, polenta and flour mixture into egg mixture until just combined.
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Spread batter evenly over oranges (preferably with an offset spatula). Bake until a wooden toothpick inserted into center comes out clean, about 1 to 1-1/4 hours. Cool in pan 5 minutes. Invert cake onto a cake plate and discard parchment.
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10
Glaze Cake:
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Heat marmalade with water in a small saucepan until melted. strain through a sieve into a small bowl. Brush top of cake with some of glaze. Serve warm or at room temperature.
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Cook's Note:
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Cake, without glaze, and be made 1 day ahead and kept, wrapped well at room temperature. Glaze before serving.
