For the filling: In a sauté pan over medium heat, add 2 T of Bellucci EVOO. Add the sliced onions and thyme. Toss to coat the onions, cover and lower the heat and cook until soft, golden and translucent. Set aside to cool.
For the pesto: In the bowl of a food processor with a metal blade, add the herbs, garlic, salt and pepper. Pulse a few times to combine. With the motor running, slowly drizzle the Bellucci EVOO through the feed tube and mix until combined
To blind-bake the tart base:
Preheat the oven to 400F. Line a large rimmed baking sheet with parchment paper or a silicone mat. Remove the sheet of puff pastry from the freezer 30 minutes before baking.
On a lightly floured work surface, roll the dough to approximately 10” x 15”. Transfer the dough onto the baking sheet. Using the tines of a fork, prick the dough all over, this will help to keep it from puffing up too much.
Place another baking sheet on top of the dough and bake for 15 minutes.
Remove the top baking sheet, again pierce any puffy lightly with a fork and return the dough to the oven and continue baking for another TK 10 minutes. Remove the pan from the oven and place on a cooling rack. Cool the tart base for approx. 20 minutes.
To assemble the tart:
Sprinkle the shredded fontina evenly across the tart base. Next, sprinkle ½ cup of the grated Parmigiano Reggiano.
Place slices of tomato in overlapping rows, on top of the cheese. Drain the liquid from the herb pesto through a fine mesh strainer. Spread the remaining herb mixture over the tomatoes.
Scatter the sautéed onions between the rows of tomatoes.
Top with the remaining grated Fontina and Parm Regg.
Bake for 30 min or until the pastry is golden brown.
Cool slightly. Serve with a crisp green salad
Place the piece of fontina in the freezer for 30 minutes before shredding. This will make it much easier to grate this creamy cheese. Remove the rind with a vegetable peeler, then use the largest (most coarse) holes on a box grater.