To make ahead: Refrigerate the orange curd (Steps 8-9) in an airtight container for up to 1 day. Bring to room temperature before assembling the cake. Refrigerate the finished cake, loosely covered with plastic wrap, for up to 3 days.
Equipment: Two 9-inch aluminum or stainless-steel (not nonstick) cake pans or cheesecake pans with straight sides and removable bottoms. Alternatively, use springform pans (make sure they're not nonstick), or use disposable 9-inch foil pie pans and carefully cut and peel the edges away to remove the baked cakes.
Tip: To improvise a double boiler, bring 2 inches of water to a simmer in a large saucepan. Then set a medium or large metal bowl over the simmering water. Allow at least 1 inch of space between the water and the bottom of the bowl.