Preheat oven to 190°C (170°C fan) / 375°F. Grease a 23cm tart or quiche tin.

Roll pastry into the tin, pressing into edges. Trim excess pastry and prick the base with a fork. Chill for 10 minutes.

Blind bake the pastry for 12 minutes using baking paper and baking beans, then remove beans and bake for another 5 minutes until lightly golden.

Meanwhile, heat olive oil in a pan and sauté onion or shallot for 3–4 minutes until softened.

Blanch asparagus in boiling water for 2 minutes, then drain and pat dry.

In a bowl, whisk eggs, cream, milk, Dijon mustard, salt, and black pepper until smooth.

Scatter salmon, asparagus, onion, and grated cheese evenly over the pastry base.

Pour egg mixture carefully into the crust.

Bake for 35–40 minutes until golden, puffed, and just set in the centre.

Cool for 10 minutes before slicing. Garnish with fresh dill or chives if desired.