Melt the butter & put it aside to cool.
Put the digestives in a zipper bag & crush the digestives w/ a rolling pin into fine crumbs.
Mix crumbs, sugar & salt.
Add the melted butter & knead it until there is a fine mess.
Put the mess in the quiche form & distribute it evenly all over the bottom & the edge with your hands & fingers by pressing.
Put the quiche form in the fridge.
Grate the zest of the lemons & set aside.
Squeeze the lemon juice - you'll need about 150 ml!
Mix the condensed milk with the lemon juice.
Whip the whipping cream w/ an electric handheld mixer until stiff.
Fold the whipping cream in the condensed milk mix.
Cool the filling in the fridge until the filling & the pastry are really cold.
Scoop the filling evenly in the cold pastry.
Sprinkle with lemon zest.
Store the pie in the fridge until it'll be served.