Make filling: Trim and slice strawberries and in a bowl stir together with sugar and lemon juice. Let strawberry mixture stand at room temperature, stirring occasionally, 4 hours. In a large sieve set over a bowl drain strawberry mixture and reserve strawberries and liquid separately.
Make custard: In a saucepan whisk together all custard ingredients except Punsch until combined well. Bring mixture to a boil over moderate heat, whisking constantly, and simmer, whisking constantly, 1 minute. Whisk Punsch into custard and transfer to a heatproof dish. Cool custard, its surface covered with a round of wax paper. Chill custard, covered, at least 3 hours, or until cold, and up to 2 days.
Make cake layers: Preheat oven to 350° F. Butter two 9- by 2-inch round cake pans and line bottoms with rounds of wax paper. Butter paper and dust pans with flour, knocking out excess flour.
Into a small bowl sift together flour, baking powder, and salt. In bowl of a standing electric mixer combine eggs and sugar and beat, beginning at moderate speed and gradually increasing to high speed, for a total of 9 to 10 minutes, or until very thick and pale and mixture forms a ribbon when beaters are lifted. Transfer egg mixture to a large bowl (for ease of folding).
Sift one third flour mixture over egg mixture and with a large rubber spatula fold in gently but thoroughly. Sift and fold remaining flour mixture into egg mixture in 2 more batches in same manner. Fold in butter and vanilla gently but thoroughly.
Divide batter between pans, smoothing tops, and bake in middle of oven, rotating pans on oven rack after 15 minutes (to ensure even baking), a total of 25 to 30 minutes, or until cake is springy to the touch and a tester comes out clean. Cool cake layers in pans on racks 10 minutes and invert onto racks. Peel off paper and cool completely. Layers may be made 1 day ahead of cake assembly and kept, wrapped tightly in plastic wrap, at room temperature.
Assemble cake: With a long serrated knife halve each cake layer horizontally to make a total of 4 layers. Put 1 cake layer, cut side up, on a serving plate and top with half of reserved strawberry slices, arranging them in an even layer. Drizzle half of reserved strawberry liquid evenly over berries.
Top filling with second cake layer, cut side down. Whisk custard until smooth and spread layer evenly with custard. Top custard with third cake layer, cut side up. Spread layer evenly with remaining strawberries and drizzle with remaining strawberry liquid. Top filling with remaining cake layer, cut side down. Chill cake, covered with plastic wrap, at least 8 hours and up to 1 day.
Make frosting: In a chilled bowl beat cream with sugar until cream just holds stiff peaks.
Spread frosting over top and sides of cake. Cake may be frosted 4 hours ahead and chilled. Bring cake to cool room temperature before serving.