Preheat your oven to 375°F (190°C). Prepare a baking sheet lined with parchment paper, tracing an 8-inch circle to guide your piping.

In a medium saucepan, combine water, milk, butter, sugar, and salt. Gently heat until the butter melts and the mixture starts steaming.

Add the flour all at once, stirring quickly with a wooden spoon until the mixture forms a cohesive ball.

Transfer the dough to a bowl and allow it to cool for about 5 minutes.

Mix in the eggs one at a time, ensuring each addition is fully incorporated.

Using a piping bag fitted with a large star tip, pipe two connected rings along the drawn circle. Create a third ring on top for added height.

Sprinkle sliced almonds on top before baking.

Bake for 35 to 40 minutes until golden brown and puffed up.

While the pastry cools on a wire rack, heat the milk in a saucepan until it simmers.

In a separate bowl, whisk together the egg yolks, sugar, and cornstarch until smooth.

Gradually whisk the hot milk into the egg mixture, then return everything to the saucepan. Cook over medium heat, stirring constantly, until thickened.

Cover the pastry cream with plastic wrap touching the surface to prevent a skin from forming, and allow it to chill completely.

Beat the softened butter until fluffy. Gradually add chilled pastry cream, mixing until combined, then add hazelnut praline paste and vanilla extract.

Carefully slice the cooled pastry horizontally.

Pipe generous swirls of the praline cream onto the bottom half, and gently place the top shell over it.

Dust with powdered sugar and sprinkle with chopped toasted hazelnuts.