Red Velvet Sheet Cake

Name: Red Velvet Sheet Cake
Prep time: 20 min
Cook time: 20 min
Total time: 40 min
Cuisine: American
Ingredients: Nonstick baking spray; 2 1/2 c. cake flour; 1 tsp. salt; 1 c. buttermilk; 1 tsp. vanilla extract; 1 tsp. baking soda; 2 whole eggs; 1 1/2 tsp. vinegar; 1 1/2 tsp. cocoa powder; 1 1/2 oz. red food coloring; 1 c. shortening; 1 3/4 c. granulated sugar; 5 tbsp. all-purpose flour; 1 c. whole milk; 2 sticks unsalted butter; 1 c. granulated sugar (not powdered sugar!); 2 c. raspberries