Ingredients
Flavorless vegetable oil for the pan
5 1/2 ounces 100% unsweetened chocolate, coarsely chopped, divided
10 tablespoons (5 ounces) unsalted butter with 82% butterfat, cut into 1-inch slices
2/3 cup (3 1/2 ounces) unbleached all-purpose flour
1/2 teaspoon kosher salt
3 (6 ounces) extra-large eggs, at room temperature
1 teaspoon pure vanilla extract, preferably Madagascar Bourbon
1 1/3 cups (10 ounces) granulated cane sugar
1/3 cup (1 1/2 ounces) walnut halves, roasted and roughly chopped