First, make the pastry. Tip the flour and butter into a food processor, and blitz to fine crumbs. Alternatively, rub the butter into the flour using your fingers. Add the egg yolk and 1 1/2 tbsp cold water, then blitz or mix until a dough comes together and forms into a ball. Shape into a disc, then cover and chill for 30 mins.

Roll the dough out on a lightly floured surface into a 1/2cm-thick circle, then use it to line a 23cm loose-bottomed tart tin, pushing it into the base and up the side. Trim any excess, then chill for another hour. Will keep chilled for a day.

Cut most of the asparagus spears into thirds, reserving 2 whole spears for decorating later. Cook the asparagus pieces in a pan of boiling water for 1 min, then drain well and immediately plunge into a bowl of iced water to halt the cooking process. Leave to cool for 15 mins, then drain well and pat dry using kitchen paper.

Meanwhile, heat the oven to 200C/180C fan/gas 6 with a baking sheet inside. Prick the pastry case all over using a fork, then scrunch up a sheet of baking parchment and use it to line the pastry case. Fill with baking beans, then carefully slide onto the hot baking sheet and bake for 15-20 mins until the pastry is set. Remove the parchment and beans, and bake for 5-10 mins more until the pastry is just starting to turn golden and is sandy to touch. Leave to cool slightly.

Separate the egg yolks and whites into two separate bowls. Melt the butter in a saucepan over a low heat, then pour into a jug. Put the yolks in a food processor and blend briefly, then, with the motor running, slowly pour in the melted butter in a thin stream until it has all been incorporated and has emulsified. (This will take 7-8 mins.) Add the vinegar and mace and blend again, then season to taste, adding a splash more vinegar, if needed. Tip the hollandaise sauce into a bowl. Beat the egg whites to stiff peaks using an electric whisk, then stir a spoonful into the hollandaise. Fold in the rest of the whipped whites in two additions, along with the capers and parsley. Spoon the mixture into the pastry case and dot over the cooked asparagus. Bake for 25-30 mins until set with a slight wobble in the centre. Leave to cool in the tin for 10-15 mins.

Peel the reserved asparagus spears into ribbons using a peeler. Pile the rocket and asparagus ribbons over the tart. Serve warm.