Preheat the oven to 180°C fan.
To make the pastry, put the flour and ½ tsp salt into a food processor. Add the butter and blitz until the mixture resembles rough breadcrumbs. Add the ice-cold water, and blitz again until the pastry is just coming together – if the pastry feels dry, add a tbsp more water and pulse again. Flatten into a disc, wrap and chill in the fridge for 30 mins until firm.
Grease the base of the tin with a little butter. Roll the pastry into a circle roughly 3mm thick on a floured surface, then use it to line a 27cm tart tin. Prick the base all over with a fork, then return to the fridge for 20 mins to firm up, or chill it in the freezer for a few minutes.
Line the pastry with baking parchment, fill with baking beans or dried rice and place on a baking tray and bake for 10 mins until the sides of the pastry are holding their shape. Remove the paper and beans and bake for 10 mins more until the pastry is lightly golden. Reduce the heat to 175°C fan.
Meanwhile blanch the nettle leaves in boiling salted water, drain and run under cold water. Squeeze out as much water as possible from the leaves then chop. (leave 2-3 leaves whole if you want to garnish the top of the tart). Remove the stalk from the wild garlic and chop finely.
Scatter the chopped nettle and garlic leaves in the pastry case, then follow with almost all the cheese. Crack the eggs into a medium bowl, and whisk lightly. Add the ricotta, cream or creme fraiche and milk, whisk again. Season lightly with salt and black pepper. Put the egg mixture into the tart and add the remaining cheese. Add a few blanched nettle leaves and garlic leaves.
Bake for 30-35 minutes or until set and golden brown. Serve warm or cold with salad.