The main difference between a Texas sheet cake and a regular chocolate sheet cake is how it is mixed together.  In most cake recipes, you’ll cream together the butter and sugars, add in the eggs slowly, and finally add in the dry ingredients and any remaining wet ingredients.  A Texas Chocolate Sheet Cake begins by bringing butter, sugar, cocoa powder, and salt to a boil, then pouring the hot ingredients into the flour mixture before mixing in the eggs and sour cream last.  It creates a super rich, chocolatey, and moist cake.