Transfer to a work area and knead with your hands until it comes together.
Wrap with cling film and let it rest for 30 minutes or more
At some point they’ll start to water out. Cook until all of their water has evaporated and then cook some more, about 5 minutes, until very fragrant and browned. Transfer in a large bowl to cool.
Transfer into the bowl with the mushrooms, add some salt and pepper, mix and let them cool for 5 minutes or more.
At this point you can either pre-bake the shells as are (no need in filling them with beans or other staff, they’ll hold their shape) or you can choose not to. If you choose to bake them, do it until they are golden brown, about 20 to 30 minutes. Then let them cool a little.
Combine the cheese with the leeks and mushrooms and divide into the pans.
Beat the milk with the eggs and a pinch of salt, and then divide it into the pans.
The recipe is for 2 tarts. You can divide it for just one tart, or better yet, divide just the ingredients for the filling and store in the freezer half of the dough for later use!