Preheat oven to 350°F.; convection oven to 325°F. Line one, half-sheet baking pan (13 x 18-inch) with parchment paper.
Combine flour, corn starch, baking powder, baking soda, salt, cinnamon, ginger and nutmeg in a large bowl until very well blended. (May prepare dry mix ahead.)
Whisk, or beat together, the buttermilk, sugar, corn syrup, melted butter, eggs, oil and vanilla extract in a large mixing bowl until smooth. Toss raisins (if using) with the flour mixture before adding the liquids. Bake an additional 5 minutes.
*If using raisins, cover with water and drain; let stand.