Start by making the choux pastry. Heat the milk and water with the salt, sugar, and butter. Once it comes to a boil, remove from heat and add the flour. Mix vigorously with a wooden spoon. Return to the heat and cook the dough until you hear a slight crackling sound—this happens quickly. Preheat the oven to 450°F (230°C).

Add the eggs one at a time, mixing well after each addition until fully incorporated. Transfer the dough to a piping bag. Pipe rows of choux so they are just touching—they will stick together as they bake. Brush with beaten egg yolk and sprinkle with sliced almonds.

Place in the oven and immediately lower the temperature to 340°F (170°C). After 20 minutes, briefly open the oven to let out steam. Bake for another 20 minutes. Once the choux are golden and puffed, remove from the oven and let cool on a wire rack.

Cut the tops off the choux and fill them with the cream using a piping bag or spoon. Replace the tops. Just before serving, dust with powdered sugar.