For the Cake:
8 oz. (1 cup) unsalted butter, softened; more for the pan
12 oz. (scant 3 cups) unbleached cake flour
2 1/2 tsp. baking powder
3/4 tsp. table salt
2 oranges
1 1/2 cups granulated sugar
1 tsp. finely grated lemon zest (from 1 lemon)
3 large eggs
1/4 tsp. pure vanilla extract
1/2 cup milk
1/3 cup fresh orange juice
For the Glaze:
1/4 cup fresh orange juice
1/4 cup packed dark brown sugar
1 Tbs. orange marmalade
For the Whipped Cream:
1 cup heavy whipping cream, well chilled
1 Tbs. confectioners' sugar
1/4 tsp. finely grated orange zest
Make the cake:
Position a rack in the center of the oven and heat to 350 degrees F. Butter the bottom and sides of a 9-inch springform pan. In a small bowl, whisk together the flour, baking powder, and salt.
Use a rasp-style grater to remove 1 tbs zest from the oranges. Juice one of the oranges to yield 1/4 cup juice.
In a stand mixer fitted with the paddle attachment, beat the butter, sugar, and orange and lemon zests on medium speed, scraping down the sides of the bowl as needed, until light and creamy, about 2 minutes. Add the eggs one at a time, beating after each addition just to combine. Add the vanilla, and beat briefly to combine.
In three additions and alternating with the milk and orange juice, add the dry ingredients, beating on medium speed after each addition and scrapping down the sides of the bowl as needed. Pour the batter into the prepared pan, tap the pan on the counter a couple of times to remove air bubbles, and smooth the surface with a spatula.
Bake until the cake is just set in the center and golden brown, 40 to 45 minutes. (A toothpick inserted in the center of the cake may have a few crumbs clinging to it.) Check the cake during the last 10 minutes of baking; if it's browning too much, tent it loosely with aluminum foil. Let the cake cool in the pan for 10 minutes, then slice a knife around the edge to release the cake, if necessary. Remove the side of the pan, and using a large cake spatula, transfer the cake from thee pan to a cooling rack. Let cool.
Glaze the cake:
Poke holes all over the cake with a toothpick in 3/4-inch intervals.
Combine the juice, sugar, and marmalade in a small saucepan over medium heat. Bring to a simmer, lower the heat to low, and whisk often until syrupy, about 10 minutes. Brush the glaze onto the cake, letting some drip down the sides. (The cake can be wrapped in plastic and kept at room temperature for up to 2 days before serving.)
Make the shipped cream and serve:
In a stand mixer fitted with the whisk attachment or in a bowl using a hand mixer, whip the cream on medium speed until it starts to thicken, about 2 minutes. Add the sugar and zest, raise the speed to medium high, and continue to whip until medium soft peaks form, about 2 minutes more. Serve the cake with the whipped cream.