Texas Sheet Cake With Chocolate Buttermilk Frosting

INGREDIENTS

2 cups

all-purpose flour (9 ounces)

2 cups

granulated sugar

1 tsp

baking soda

1/4 tsp

salt

1 cup

butter

1/3 cup

unsweetened cocoa powder (not Dutch process)

large eggs

1/2 cup

buttermilk (see below for substitutes)

1 1/2 tsp

vanilla extract

Chocolate Frosting:

1/4 cup

butter

3 tbsp

unsweetened cocoa powder

1/3 cup

buttermilk, or as needed

1 lb

confectioners' sugar, about 3 1/2 cups

1/2 tsp

vanilla extract

1/2 cup

chopped pecans, optional