Corn Potage

Name: Corn Potage
Ingredients: 2 cups grapeseed oil; 6 large egg yolks; 5 ears fresh corn (about 2 pounds), shucked, kernels cut off, cobs reserved; 1 quart whole milk; 1 large yellow onion (about 1 pound), thinly sliced; 1/2 cup (4 ounces) unsalted butter, cut into 4 pieces; 1 tablespoon kosher salt, plus more to taste; Granulated sugar, to taste; Finely ground black pepper, for serving