Make sure you remove the puff pastry from the freezer in advance. I like to thaw it in the fridge overnight but if you leave it out at room temperature for a couple of hours, that should be fine. Make sure it's still somewhat chilled when you go to bake it though.
Place the milk in a saucepan over medium-low heat and allow it to come to a simmer.
1 cup (240mL) whole milk
Meanwhile place the egg yolks and sugar in a medium bowl and whisk aggressively for 1-2 minutes while the milk heats.
4 large egg yolks, 1/2 cup (100g) granulated sugar
Remove the milk from the heat and stream half of it into the egg mixture, while whisking, to temper the eggs.
Then add the egg mixture to the saucepan with the rest of the milk and cook over low heat for 5-10 minutes, while whisking continuously (doesn’t have to be aggressive whisking just keep it moving the whole time).
The custard won’t thicken significantly but it should thicken slightly. To test if the custard is done cooking, it should coat the back of a spoon and when you draw a line through it (on the back of the spoon) the line stays separated. You can also use a thermometer and bring the cream to about 180F-185F.
Pour the custard back into a large bowl, add the butter and vanilla and mix just until they're all combined.
2 Tbsp (28g) salted butter, 2 tsp vanilla bean paste
In a small bowl, mix together the gelatin and water until they’re combined. Let it set and then microwave it for 10 seconds. Mix and then add it to the custard. Whisk the gelatin well with the custard and then cover the surface with plastic wrap. Refrigerate for about 2 hours until the custard feels somewhat set and still a little jiggly but not runny.
1 Tbsp (9g) gelatin
During this time, preheat your oven to 425F.
Place your sheet of puff pastry onto a cookie sheet and spread it out just slightly, about an extra inch on each end to make it a little longer (I just use my fingers to gently press on it, a rolling pin also works).
1 sheet of puff pastry
Bake the puff pastry for 10 minutes and then reduce the temperature to 350F for 10 minutes or until it’s browned on top (it should be puffed like my photo).
Remove the puff pastry from the oven and set it aside to cool completely. Once it’s cooled, use a large serrated knife to slice the puff pastry in half (I like to leave just a little more on the bottom than the top), making a bottom half and a top half. Press the insides of the bottom half down to flatten it a little and the edges should come up a little creating a small barrier around the edge for the cream to sit in.
Place the top half in a bowl (or pan) and use your hands to crush it into tiny little pieces. Set aside.
When the custard is ready, sift the powdered sugar into the bowl of a stand mixer (or a large bowl with a hand mixer). Add heavy whipping cream and mix on medium-low speed until it thickens a little, about 30 seconds. Increase the speed to medium-high and beat for just another 30-60 seconds, until the cream holds stiff peaks. Don’t over-mix.
1/3 cup (40g) powdered sugar, 1 1/2 cups (13oz) heavy whipping cream
Remove the custard from the fridge and use a whisk to mix it until it’s smooth again. This will disrupt the gelatin but it will set again when we put it back into the fridge. Make sure you whisk it until there are no more lumps and the custard is smooth again.
Add 1/3 of the whipped cream to the custard and whisk until it’s completely smooth. Add another 1/3 of the heavy whipping cream to the custard and now use a rubber spatula to fold it in gently. Repeat with the last 1/3.
Spread the mixture onto the bottom half of your puff pastry. It’ll be tall but it should be thick enough not to spill past the edge of the puff pastry. Cover the top of the cream with the crushed puff pastry.
Refrigerate for at least 4 hours or overnight. Dust with powdered sugar before serving.