Hi Martha! We've had success making three tiers using this recipe. Susan, the post author, recommends inserting some "milkshake-style" straws into the centers to add a little extra support if you're going any higher than three tiers. The 9" x 13" should be ok, if you're able to put a parchment paper sling into your baking sheet to easily lift the cake out once it's cool that will help things. Annabelle@KAF

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