Preheat the oven to 200 degrees Celsius / 400 degrees Fahrenheit
Sieve the flour and a large pinch of sea salt into a bowl and add the cold butter in small chunks. Rub the butter and flour together using your fingertips together until it looks like breadcrumbs.
Mix the egg yolk with the water and begin adding it tablespoon by tablespoon to the flour/butter mixture until you have a ball of pastry dough that has a slight sheen to it and any dry crumbs have been incorporated.
Roll the pastry out into a large circle and line a tart tin with it. Prick the base of the shortcrust pastry a few times all over it with a fork.
Line the inside of the pastry case with a baking paper cartouche and fill with baking beads (or use uncooked rice if you don't have any).
Blind bake the shortcrust pastry case on an oven tray for 20 minutes, then remove the baking beads and put the pastry case back in the oven for a further 5-10 minutes until it is cooked through and a light golden brown.
Cut your asparagus spears into 1-inch pieces and blanch them in boiling water for 1 minute before immediately removing them to a bowl of ice-cold water to halt the cooking process.
Heat some cooking oil in a frying pan and fry the prosciutto slices until they are dark and crispy. Drain the crispy prosciutto on kitchen paper, then break into small pieces.
Mix the cream, milk, egg, and egg yolk together and season with salt and pepper. Strain the savory custard through a sieve into a jug. Stir through finely diced mint leaves.
Turn the oven down to 180 degrees Celsius / 350 degrees Fahrenheit.
Place half your asparagus and crispy prosciutto into the shortcrust pastry tart case, and pour half of the savory egg custard quiche filling on top. Repeat and try and fill the shortcrust pastry quiche case as high as you can without it spilling over the edge.
Bake the asparagus and crispy prosciutto quiche for 25 - 30 minutes or until the filling is set and starting to souffle up in the middle.
Remove the asparagus and crispy prosciutto quiche from the oven and allow to cool slightly before serving.