Preheat the oven to 180°C. Bring the milk to a boil with the salt and butter. Remove from heat, add the flour all at once and mix until the dough forms a ball that pulls away from the bottom. Put the pan back on the heat to dry the dough. Remove from heat. Add 2 eggs one at a time (110 g in total) and mix well each time until a homogeneous, not too runny dough forms. Pour it into a piping bag.
Pipe small mounds of dough the size of a nut onto the baking sheet lined with parchment paper, not too close together. Brush them with the 3rd beaten egg and bake for 25 minutes until golden brown in the oven. Let cool.
Put the drained red salmon in the blender cup and add the smoked salmon, along with the chopped hard-boiled egg, mayonnaise, Philadelphia, chopped chives, 1 tsp grated lemon zest, and pepper. Blend until a homogeneous mousse; adjust seasoning further. Pour into a piping bag with a star nozzle.
Open the profiteroles and fill them with mousse. Lightly press the vertically cut tops on. Finish with salmon roe, chives, and dill. Serve chilled.
Tips
Do not fill the puffs too long in advance, otherwise they will be too soft.