In a bowl, mix the flour and sugar. Add the softened butter and rub it in until it forms a crumbly texture. Add the egg yolks and knead until the dough comes together. Wrap the dough in plastic wrap and chill in the fridge for about 30 minutes.
In a saucepan, melt the butter with the water over medium heat. Once melted, add the flour all at once and stir quickly until the dough forms a ball. Cook for another 1-2 minutes. Remove from heat and let it cool slightly. Beat the eggs in a separate bowl and slowly add them to the dough, stirring until smooth.
Preheat your oven to 400°F (200°C). Roll out the pâte sucrée dough and line a tart pan with it, pressing it into the edges. Bake it for 10-12 minutes, or until golden. Meanwhile, pipe the choux pastry into small balls and place them on a baking sheet. Bake for 15-20 minutes or until they’re golden and puffed up. Let them cool.
In a saucepan, heat the milk until it’s just about to boil. In a separate bowl, whisk together the egg yolks, sugar, flour, and cornstarch until smooth. Gradually add the hot milk to the egg mixture, whisking constantly to avoid curdling. Pour it back into the saucepan and cook over low heat until it thickens. Remove from heat and stir in the vanilla extract. Let it cool, then fold in the lightly whipped heavy cream.
Once the pastry cream is ready and cooled, spread a layer inside the tart crust. Cut a small hole in the bottom of the choux buns and fill them with the cream. Arrange the filled choux around the edge of the tart, creating a ring.
In a saucepan, heat the sugar and water over medium heat until it turns golden. Be careful not to burn it. Once the caramel is ready, use a spoon to drizzle it over the choux puffs to hold them in place.
Make Spun Sugar: To add a beautiful finishing touch, heat some extra sugar in a pan until it melts and forms a caramel. Once it reaches the right consistency, you can use a whisk to spin it onto a parchment paper sheet, creating delicate sugar threads to top your cake.
Allow the caramel to set before serving. The result should be a stunning Gâteau Saint Honoré with shiny caramel-coated choux, a smooth pastry cream center, and a delicate, sweet flavor in every bite.
