Choux Pastry:

Preheat the oven to 400°F (200°C).
In a saucepan, combine the water, milk, salt, and butter cut into pieces.
Melt the butter and bring to a boil.
Remove from heat, add the flour all at once, and mix well. Return to low heat.
Stir until the dough dries out and pulls away from the sides of the pan.
Transfer the dough to a stand mixer fitted with the paddle attachment and mix on medium speed to cool it slightly.
Meanwhile, beat the eggs with a fork and gradually add them to the dough, mixing until smooth.

Using a piping bag, pipe a ring of dough onto a baking sheet, then pipe a second ring inside the first, and finally a third ring on top of the first two.
Sprinkle with sliced almonds.
Bake for about 40 minutes.
Let cool completely.

Praline Mousseline Cream:

Pour the milk into a saucepan and bring to a boil.
Meanwhile, whisk the egg yolks with the sugar until pale.
Add the custard powder or cornstarch.
Gradually pour the hot milk over the egg mixture, whisking constantly.
Return the mixture to the saucepan and cook for about 2 minutes, stirring constantly, until thickened.
Let cool completely.
Place the softened butter in a stand mixer with the paddle attachment and beat until creamy.
Gradually add the cooled pastry cream.
Finally, add the praline paste and mix until smooth.

Transfer the mousseline cream to a piping bag fitted with a star tip.
Slice the choux pastry ring in half horizontally with a serrated knife.
Pipe the mousseline cream onto the bottom half of the pastry, then gently place the top half back on.
Dust with powdered sugar.