Instructions

for the pastry cream

Sprinkle gelatin over water in small bowl and let sit until gelatin softens, about 5 minutes. Whisk egg yolks, sugar, and salt in medium bowl until pale yellow. Whisk 1/4 cup milk and cornstarch into egg mixture until smooth. Heat remaining 1 1/2 cups milk in medium saucepan over medium heat until hot but not simmering. Slowly whisk hot milk into egg mixture.
Transfer egg mixture back to saucepan and cook over medium-low heat, whisking constantly, until mixture thickens to pudding consistency, about 5 minutes. Off heat, vigorously whisk in gelatin mixture until dissolved. (If pastry cream is lumpy, strain through fine-mesh strainer.) Transfer pastry cream to clean bowl and whisk in butter and vanilla. Cover and refrigerate until firm, at least 3 hours or up to 24 hours.

for the cake

Grease large bowl. Whisk milk and egg and yolks together in 2-cup liquid measuring cup until combined. Using stand mixer fitted with dough hook, mix flour, sugar, yeast, and salt together on medium-low speed until combined, about 5 seconds. With mixer running, slowly add milk mixture and knead until cohesive dough forms and no dry flour remains, 3 to 5 minutes, scraping down bowl and dough hook as needed.
With mixer still running, add butter 1 piece at a time until incorporated. Continue kneading until dough is uniformly combined, 8 to 10 minutes (dough will be sticky and will not completely clear sides of bowl). Turn out dough onto lightly floured counter and knead until smooth, about 1 minute. Form dough into tight ball and transfer to greased bowl, turning to coat. Cover with plastic wrap and let rise at room temperature until nearly doubled in size, 1 to 1 1/2 hours.
Grease light-colored 9-inch round cake pan, line with parchment paper, and grease parchment. Transfer dough to lightly floured counter and press into 9-inch round. Transfer dough to prepared pan and press in even layer to edges of pan. Using fork, poke dough all over. Cover pan loosely with plastic and let rise at room temperature until puffy, 35 to 50 minutes. (After rising, dough and pan can be wrapped tightly in plastic and refrigerated for up to 24 hours. Let dough come to room temperature before baking.)

for the topping

Meanwhile, bring butter, honey, sugar, and salt to boil in small saucepan over medium heat, stirring often. Once boiling, stir in almonds and remove from heat.
Adjust oven rack to middle position and heat oven to 350 degrees. Spread almond mixture evenly over top of dough. Bake until topping is deep golden brown, 30 to 40 minutes, rotating pan halfway through baking. Let cake cool in pan on wire rack for 20 minutes. Remove cake from pan and let cool completely on rack, about 2 hours.
Stir chilled pastry cream with fork to loosen. Transfer cake to cutting board topping side up. Using long serrated knife, split cake in half horizontally. Transfer cake bottom to serving platter and spread pastry cream evenly over cut side. Cut cake top into 12 wedges and reassemble on top of pastry cream. To serve, use cuts in top layer as guide to slice cake into 12 pieces.