Prepare the choux pastry:

On 3 sheets of parchment paper, trace 16 circles, each 2 3/4 inches (7 cm) in diameter, using a pencil. Flip the sheets over so the dough doesn't touch the pencil marks. Prepare three baking sheets by turning them upside down and placing the parchment on top.
Prepare two piping bags: one fitted with a plain 1/2-inch (13 mm) tip for the choux, and the other with a star tip (8 or 10 mm) for the cream.
Let the butter come to room temperature for the mousseline cream.

Preheat the oven to 350°F (180°C), conventional heat.

Crack the eggs into a bowl and beat lightly with a fork. Place the flour in a separate bowl.

In a saucepan, heat the water, milk, salt, and butter.
When it comes to a boil, remove from heat and add all the flour at once. Return to the heat and stir vigorously with a spatula to dry out the dough.

Transfer the dough to the bowl of a stand mixer fitted with the whisk attachment and whisk to let the steam escape. Once the steam has dissipated, add the beaten eggs gradually while continuing to whisk.
When the dough is smooth, transfer it to a piping bag and pipe open rings using the pencil guides you drew earlier.

Brush the rings with egg yolk to smooth the surface and prevent air bubbles.
Sprinkle with sliced almonds.
Bake for 35–40 minutes without opening the oven door.
Let cool before slicing horizontally.

For the mousseline cream:

Line a tray with plastic wrap, leaving extra at the end.
Heat the milk.
Meanwhile, mix the eggs and sugar, then add the cornstarch.
Pour the hot milk over this mixture and return everything to the saucepan.
Stir until it comes to a boil.

Pour the cream onto the plastic wrap–lined tray and cover with the extra wrap, smoothing it out to help it cool quickly and remove air bubbles. Cut the wrap and chill in the refrigerator.

When the reserved butter and pastry cream are at the same temperature: using a stand mixer with the whisk attachment, gently whisk the pastry cream to loosen it. Gradually add the butter, cut into small pieces, then the praline paste. Make sure the mixture is smooth and homogeneous before transferring to a piping bag (the one fitted with the star tip). Fill the choux rings immediately if the cream is firm; if it's a bit soft, chill before filling.