Slice tomatoes in halves and lay out on paper towels.
Sprinkle very generously with salt.
Allow tomatoes to set out at least 1 hour before using.
Meanwhile, in large cast-iron skillet heat olive oil over medium heat.
Add leeks, garlic, mushrooms, and green onions and sauté about 5-10 minutes until veggies are soft.
Roll out pastry and gently fit pastry into about 15 tart pans.
Using a knife, cut off any excess pastry around the edge.
Once tomatoes have set out at least an hour and liquid has drained out of them begin filling tarts.
Don’t fill the tarts until everything is ready or the crusts will get soggy.
Spread the leek/mushroom mixture evenly among all the tart pans.
Sprinkle the Parmesan, Fontina, and Asiago cheeses evenly over the leek mixture in each pan trying to divide the cheese as evenly as possible among all the tart pans.
Layer a slice of the large tomato in each tart pan.
Then layer the heirloom, cherry and grape tomatoes into the tart pans using up all of the tomatoes.
You may need to overlap or double stack the tomatoes.
Sprinkle a few pinches of basil, oregano, rubbed sage leaves, thyme, and rosemary over top of the tomatoes.
If desired, season with salt and pepper.
Sprinkle the finely grated pecorino romano cheese over top of the tarts.
Bake tarts at 350° for about 20 minutes or until cooked through.