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Galvanized metal is zinc coated. When zinc is heated, it produced harmful fumes. I know it's dangerous to inhale these fumes, and probably not good to eat them either.
We also know "vanilla essence" as "vanilla extract", or as most recipes call it "pure vanilla extract". I can't help but think what would happen if you used "impure vanilla extract"! ;)
Of most interest to me is the use of "self-raising" flour. Note to Americans... it is NOT the same as "self-rising" flour. According to America's Test Kitchen, "self-raising flour is made by adding 2 teaspoons of baking powder to each cup of all-purpose flour." That works out to about 9 grams baking powder per 125 grams of all-purpose flour.Self-rising flour doesn't give the same lift. Substitute with care.
If you weigh your ingredients it's not a problem. Just make sure you cream your sugar and butter well in the cake part. The syrup won't matter, since it's dissolved in solution.