Lightly butter and flour either one 10-cup Great Pumpkin Pan (available from Williams-Sonoma; williamssonoma.com) or 3 round cake pans — 6, 8, and 10 inches. (If making the tiered cake, plan also to double the recipe.) Take care to cover all crevices and corners.
Place all of the ingredients plus 3/4 cup water in a large mixing bowl and beat, using a mixer set on medium-high speed, until batter is smooth.
Fill the cake pan(s). (For Great Pumpkin Pan, divide batter evenly between the two halves; for round cake pans, divide batter evenly.) Bake until a skewer inserted into the center tests clean — about 35 minutes for the pumpkin cakes; 25 minutes for the 6-inch, 30 minutes for the 8-inch, and 35 minutes for the 10-inch layers of the tiered cake. Cool completely on a wire rack before frosting or decorating.
Trim the pumpkin cake halves before stacking together to form the pumpkin-shaped cake. Stack tiers, spreading frosting between layers. To make the simple frosting shown above, whisk 1 cup confectioners’ sugar with 2 to 3 tablespoons lemon juice until it’s the consistency of molasses. Drizzle over cake.