Preheat oven to 220°C/425°F/Gas Mark 7.

Cook asparagus in salted water or steam for 3 minutes until just tender.

Drain asparagus and immerse in cool water to stop cooking.

Unroll puff pastry and trim the outer edges.

Cut the pastry in half lengthwise to create two long rectangles.

Place pastry rectangles on a baking sheet.

Brush the pastry with beaten egg.

Lay prosciutto slices on top of the pastry.

Arrange the cooked asparagus on top of the prosciutto.

Brush everything with beaten egg again.

Bake in the preheated oven for 15-20 minutes, or until puffed and golden brown.

While the pastries are baking, poach the eggs.

Add white wine vinegar to a pan with 500ml of water and bring to a simmer.

Crack an egg into a teacup.

Swirl the water in the pan and gently slip the egg from the teacup into the center.

Poach the egg for 2 minutes.

Remove the poached egg with a slotted spoon and place in cool water.

Repeat the poaching process for all eggs.

Reheat the poached eggs in simmering water for 1 minute before serving.

Top the baked tarts with the poached eggs.

Sprinkle with black pepper and sea salt.

Serve immediately, optionally with dressed spring salad leaves.