Make the choux pastry: Preheat oven to 340 degrees.
In a saucepan, add water, milk, butter, sugar and salt. Bring to a boil, then remove from heat. Add the flour and mix vigorously with a wooden spoon. Return the pan to the heat for 2 minutes, stirring constantly, then remove from heat and let it cool for 2 minutes.
Break the eggs into a large mixing bowl, then add the pastry mix and whisk until smooth. Mixture should hold its shape when a finger is run through it. Transfer into a piping bag fitted with a 1/2-inch round tip.
Pipe 6 large balls inside each donut ring, making sure they meet up fully in a circle. Brush the tops with egg wash, then bake for 25 minutes. Brush each pastry ring with egg wash again, then sprinkle with almonds. Bake for another 5 minutes, then place on a wire rack to cool.
Make the praline: Finely slice the hazelnuts and toast them for 5 minutes in a saucepan, then allow to cool. Line a baking tray with parchment paper.
In a saucepan, add the sugar and water. Stir until the sugar has dissolved. Bring to a fast boil, keeping watch over it until it turns a dark amber color. Remove from heat and stir in the toasted nuts, then pour onto the parchment paper and allow to cool. Once cool, blitz half of the praline to a fine powder in a spice grinder or food processor. Chop the remaining praline into small pieces and set aside.
To assemble: When the pastry is cool, cut each one into two pieces by slicing horizontally through the middle. Whip the cream to soft peaks then fold in the ground praline. Whip the cream again slightly, if needed, to bring it to a firm piping consistency, and transfer it into a piping bag fitted with a large star tip. Pipe rosettes of cream all around the bottom half of the pastry, then add a sprinkling of chopped pralines before adding the lid. Top with sliced almonds, dust with powdered sugar and serve.