Preheat oven to 350°. Spray a 13x9-inch baking dish with baking spray with flour.
In a large bowl, beat shortening and sugar with a mixer at medium-high speed until fluffy,
to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition.
In a medium bowl, whisk together flour, cocoa, salt, and baking soda. With mixer on low speed, gradually add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating just until combined after each addition. Beat in food coloring, vinegar, and vanilla. Pour batter into prepared pan, smoothing top with an offset spatula.
Bake until a wooden pick inserted in center comes out clean, 20 to 25 minutes. Let cool completely on a wire rack. Top with White Chocolate Frosting. Garnish with white chocolate curls, if desired.
Notes
*We used Swans Down.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/red-velvet-sheet-cake-recipe/