Gemma's Best Brownie Recipe (One Bowl, Crackly Top)

Name: Gemma's Best Brownie Recipe (One Bowl, Crackly Top)
Prep time: 25 min
Cook time: 30 min
Total time: 55 min
Cuisine: American
Ingredients: 4 large eggs, cold; 1 cup plus 2 tablespoons ((8 ¼ oz/227 g) granulated sugar); 1 cup plus 2 tablespoons (6 ¼ oz/177 g) (dark brown sugar); 1 cup (8 oz/225 g) butter, (melted ); 2 tablespoons vegetable oil; 4 teaspoons vanilla extract; 1 teaspoon salt; 1 cup (5 oz/142 g) all-purpose flour; 1 cup (4 oz/115 g) unsweetened cocoa powder; 1 ½ cups (9 oz/255 g) roughly chopped bittersweet chocolate, (divided in half)