Brown Sugar Sheet Cake

Name: Brown Sugar Sheet Cake
Cook time: 1 h
Total time: 1 h
Cuisine: American
Ingredients: 3 cups all-purpose flour; 1 3/4 cups brown sugar; 3/4 cup sugar; 1 1/2 cups (3 sticks) unsalted butter, room temperature; 3 eggs, lightly beaten; 3/4 cup greek yogurt; 3 teaspoons vanilla extract; 1 1/2 teaspoons baking soda; 1 teaspoon salt; 4-6 cups powdered sugar, as needed; 1 1/2 cups dark brown sugar; 3/4 cup (1 1/2 sticks) unsalted butter; 1/2-1 cup whole milk, warmed; 1 teaspoon vanilla extract; 1/2 teaspoon salt