Build yourself a golden Lemon-Thyme Tower Cake featuring layers of rich, tart lemon cake filled with lemon-thyme pastry cream and decorated with slices of sweet candied lemons for a dessert that is equal parts refined and rustic.
Heat oven to 375 degrees. Butter and flour three 6-inch-round cake pans, and set aside.
Combine eggs, sugar, salt, and lemon zest in the bowl of an electric mixer fitted with the whisk attachment. Mix on high speed until pale and fluffy, about 5 minutes. Sift flour and cornstarch over egg mixture; fold in with a rubber spatula. Pour batter into pans.
Bake until cakes spring back to the touch and cakes begin to pull away from sides of pans, 40 to 45 minutes. Remove cakes from oven; transfer to a wire rack to cool.
Turn out cakes. Using a serrated knife, level the tops; slice each cake horizontally into two even layers. Place one layer on a 6-inch cardboard round. Using a pastry brush, brush 5 layers generously with the candied-lemon syrup. Spread the pastry cream over 5 layers, about 3/4 cup per layer. Stack layers on the cardboard, ending with the one uncoated layer. To stabilize cake, insert a 6-inch wooden skewer through center. Overlap the candied lemon slices and thyme sprigs on top of the cake. Refrigerate until pastry cream has set, at least 1 hour. Serve.