Prepare the pastry:
Preheat the oven to 170°C (fan). Lightly grease the base and sides of a 25 cm tart pan. Lay in the pastry, trimming the edges, and bake for 15 minutes. Remove and let it cool for 10 minutes.

Prepare the salmon:
Dice the salmon and keep it covered in the fridge until ready to use.

Cook the vegetables:
In a pan, combine the leeks, carrots, and ½ cup of water. Cook over medium heat until the vegetables have absorbed the liquid and the leeks are soft.
Add a few drops of olive oil and the spring onions, sauté for 2–3 minutes, then remove from heat.

Make the creamy filling:
In a bowl, whisk together the eggs, yogurt, and mustard. Season with salt, pepper, and dill.

Assemble the tart:
Spread the sautéed vegetables evenly over the partially baked tart shell. Add the diced salmon on top, then carefully pour the egg-yogurt mixture over everything.

Bake:
Bake the tart on the middle rack of the oven for about 35 minutes, until the filling is set and the surface lightly golden.

Serve:
Let the tart cool for 15 minutes before serving. Garnish with a sprinkle of chives.