Old Fashioned Chocolate Sheet Cake

Cake
2 Preheat the oven to 350F.
3 Grease a 13x9-inch pan and dust with cocoa. Set aside.
4 Combine the cocoa, flour, baking powder, and salt in a bowl and set aside.
5 Beat the butter and sugar until light and fluffy - about[timer minutes=0] 2 minutes[/timer]
6 Add eggs, one at a time, and beat well after each.
7 Stir in the vanilla.
8 With mixer on low blend in 1/3 of the flour mixture.
9 Add 1/2 the sour cream.
10 Blend in 1/3 of the flour mixture.
11 Add the rest of the sour cream.
12 Stir in the remaining flour mixture.
13 Spoon batter into the prepared pan.
14 Bake for [timer minutes=0]30 to 35 minutes[/timer], or until done.
15 Cool.
Frosting
18 Add the cream, pudding mix, and powdered sugar to the bowl of a mixer.
19 Whip until light and fluffy.
20 Spread thickly on cooled cake.