1 1/4 cups sugar
3 large eggs
1 cup all-purpose flour (spooned and leveled)
1/4 cup Dutch-process cocoa powder (spooned and leveled)
1/2 teaspoon salt
4 tablespoons (1/2 stick) unsalted butter
1/4 cup heavy cream
8 ounces bittersweet chocolate, coarsely chopped
Preheat oven to 350 degrees. In a large bowl, whisk together sugar and eggs. In another bowl, whisk together flour, cocoa, and salt.
In a medium ovenproof nonstick skillet, bring butter and cream to a simmer over medium. Add chocolate; reduce to medium-low. Cook, stirring constantly, until chocolate has melted, about 1 minute. Remove from heat, and let cool 5 minutes.
Add chocolate mixture to sugar mixture, whisking until blended (reserve skillet). Fold in flour mixture. Pour batter into skillet.
Bake until a toothpick inserted in center comes out clean, about 40 minutes. Serve from skillet, warm or at room temperature.