Red Velvet Sheet Cake

Name: Red Velvet Sheet Cake
Ingredients: Nonstick vegetable oil spray; 3 oz. unsweetened chocolate, chopped; ¾ cup sour cream; 1 Tbsp. plus 1 tsp. liquid red food coloring; 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt; 2 tsp. vanilla bean paste or vanilla extract; 2 cups (250 g) bleached all-purpose flour; 1¾ cups (packed; 350 g) light brown sugar; 1 tsp. baking powder; 1 tsp. baking soda; ¾ cup (1½ sticks) unsalted butter, cut into 1 pieces, room temperature; 3 large eggs, lightly beaten to blend; 8 oz. cream cheese, room temperature; ½ cup (1 stick) unsalted butter, room temperature; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt; 1 cup (110 g) powdered sugar; ¼ cup chilled heavy cream; Flaky sea salt and sprinkles (for serving; optional)