Old-Fashioned Hot Fudge Sundae Cake

Name: Old-Fashioned Hot Fudge Sundae Cake
Cuisine: American, Southern
Ingredients: 1 cup all-purpose flour; 3/4 cup sugar (granulated sugar); 2 Tablespoons baking cocoa (unsweetened); 2 teaspoons baking powder; 1/4 teaspoon salt; 1/2 cup whole milk; 2 Tablespoons vegetable oil; 1 teaspoon pure vanilla extract; 1 cup chopped nuts (pecans or walnuts), optional; 1 cup light brown sugar (packed); 1/4 cup baking cocoa (unsweetened); 1 3/4 cups very hot water