Fit the mixer with its dough hook and combine the flour, sugar, yeast, lemon zest, and salt in its bowl, then gently heat the milk, butter, and vanilla in a small saucepan over low heat. Once the butter has just melted, take the saucepan off the heat, let it cool for 2–3 minutes, and add the liquid to the flour mixture.

Run the mixer for 5 minutes, round the dough into a ball, cover it with plastic wrap, and return it to the bowl beneath a clean kitchen towel for a 1-hour rise in a warm spot. The kneaded dough should feel smooth and supple, and the resting dough should visibly expand.

During the rise, whisk 100 ml of the filling milk with the cornstarch, sugar, egg yolks, and vanilla in a large bowl, then warm the remaining milk and the cream over medium heat. Watch for small bubbles around the saucepan’s edge before adding the cold mixture.

Add the cornstarch mixture to the heated dairy and whisk continuously without boiling, then take the thickened custard off the heat and beat in the butter. Transfer the smooth filling to the bowl, lay plastic wrap against its surface, and let it cool completely at room temperature without prolonged unrefrigerated holding.

After the first rise, preheat the oven to 180 °C / 350 °F / Gas 4, line the springform base with parchment, grease its sides, and roll the dough on a lightly floured surface into a 26 cm circle. Fit the dough into the 26 cm (10 in.) pan, cover it, and give it a second rise of 15 minutes.

During this second rise, heat the topping butter, cream, sugar, and honey together, stirring as the mixture reaches a simmer, then maintain the simmer for 2 minutes. The sugar should dissolve before you fold in the almonds and remove the saucepan from the heat.

Distribute the almond topping across the dough and bake for 30 minutes, then leave the cake in its pan for 5 minutes before running a small sharp knife around the edge and releasing the ring. The cake should have risen and turned golden brown; leave it to cool completely before cutting.

Slice the fully cooled cake horizontally with a serrated knife, lift away the almond-covered half, and put the lower half on a serving plate. Refit the springform ring around the bottom layer so it can contain the custard.

Beat the cooled custard with an electric beater until smooth, spread it over the enclosed bottom layer, and refrigerate the filled layer for at least 1 hour. The filling needs this full setting period even though the almond lid will go on partway through.

Cut the separate almond lid into 8 equal wedges with a sharp knife, then arrange them over the filling after the bottom layer has chilled for 30 minutes. Continue chilling until the full minimum 1-hour setting time is complete, and serve the cake chilled.