Preheat the oven to 350°F (180°C).
For the praline mousse cream:
1 Heat the milk in the saucepan.
2 At the same time, whisk the egg yolks with the sugar in a bowl, then add the flour.
3 Pour over the hot milk, whisking constantly, then add everything back into the saucepan.
4 Cook while whisking until the cream thickens, then add 2.1 oz of butter off the heat and leave to cool.
5 Vigorously whisk 2.1 oz butter and 2.1 oz praline in a bowl, then add to the pastry cream. Leave to cool completely.
6 Emulsify the cream with a whisk or beater to obtain a mousse-like texture and add to a pastry bag.
7 In the saucepan, add the water, sugar, butter and heat over medium heat, stirring with a spatula.
8 When the mixture comes to a simmer, remove the saucepan from the heat and tip in the flour in one go.
9 Mix vigorously with the spatula, and continue stirring over medium-low heat.
10 Stir to dry out the dough, until it forms a ball, then remove from the heat, continuing to stir to cool the choux pastry down.
11 Once cooled, add the eggs, one at a time, and add the choux pastry to a piping bag and pipe the choux buns onto a cookie sheet covered with parchment paper.
12 Bake for 20 to 25 minutes and leave to cool.
13 Cut the choux buns 2/3 of the way through and fill with the cream.
Tip: You can replace the praline with chocolate spread.