Instructions

MAKE THE CANDIED RHUBARB:
1. In a medium saucepan, combine sugar, water, split vanilla bean (and seeds), and lemon peel.
2. Bring to a boil, stirring until sugar dissolves, then reduce heat to low simmer.
3. Add rhubarb pieces and poach gently for 3-5 minutes until just tender but still holding their shape.
4. Remove rhubarb with a slotted spoon and let cool on a wire rack. Reserve syrup.
5. For crystallized effect, you can roll warm rhubarb pieces in granulated sugar and let dry.

MAKE THE THICK CRÈME PÂTISSIÈRE:
6. In a medium saucepan, heat milk with vanilla bean and seeds (or extract) until just below simmering. Remove from heat.
7. In a bowl, whisk together egg yolks and sugar until pale and thick.
8. Whisk in cornstarch, flour, and salt until smooth with no lumps.
9. Slowly pour half the hot milk into the egg mixture, whisking constantly to temper.
10. Pour the mixture back into the saucepan with remaining milk.
11. Cook over medium heat, whisking constantly and vigorously, until mixture thickens considerably and comes to a boil.
12. Boil for 1-2 minutes while continuing to whisk to cook out the starch flavor.
13. Remove from heat and whisk in butter until melted and incorporated.
14. Strain through fine-mesh sieve into a bowl. Press plastic wrap directly onto surface to prevent skin formation.
15. Refrigerate until completely cold and set, at least 2 hours. The custard should be firm enough to pipe or spread without running.

MAKE THE SPONGE CAKE:
16. Preheat oven to 350°F. Grease and line two 8-inch round cake pans with parchment paper.
17. In a medium bowl, whisk together flour, baking powder, and salt.
18. In a large bowl, cream butter and sugar until light and fluffy, about 4-5 minutes.
19. Beat in eggs one at a time, mixing well after each addition. Add vanilla and lemon zest.
20. Add flour mixture in three additions, alternating with milk in two additions, beginning and ending with flour. Mix just until combined.
21. Divide batter evenly between prepared pans and smooth tops.
22. Bake 25-30 minutes until golden and a toothpick inserted in center comes out clean.
23. Cool in pans for 10 minutes, then turn out onto wire racks to cool completely.

ASSEMBLE THE CAKE:
24. Once custard is completely chilled and set firm, whisk briefly to loosen slightly for spreading.
25. Place one cake layer on serving plate. Spread with half the thick crème pâtissière, leaving a 1/2-inch border.
26. Arrange some candied rhubarb pieces on top of the custard.
27. Top with second cake layer.
28. Spread remaining custard on top or pipe decoratively.
29. Arrange remaining candied rhubarb pieces artistically on top.
30. Dust lightly with powdered sugar.
31. Refrigerate until ready to serve, at least 30 minutes to allow layers to set.