Brush six 5 ¾-by-3 ½-inch disposable loaf pans with the melted butter. Position a rack in lower third of oven. Preheat oven to 350° F.
Sift the flour, cornstarch, baking powder, salt, and nutmeg into a large bowl; set aside.
In the bowl of an electric mixer, beat the room-temperature butter on medium until smooth. Gradually add the sugar and beat until fluffy, about 3 minutes. Lightly whisk the eggs, then beat them into the butter-sugar mixture. Add the lemon zest. Add a quarter of the dry-ingredients mixture, followed by a third of the cream, blending until smooth. Repeat until all the dry ingredients and cream have been combined. Blend in the extracts.
Divide the batter among the pans. Place pans in oven, spacing evenly. Bake 40 to 45 minutes or until the tops are golden and a toothpick comes out clean. Transfer to a cooling rack. The cakes can be wrapped in plastic and kept frozen for up to 1 month.