Tart Crust

In a medium bowl, mix together flour and salt. Add butter with a pastry blender until crumbly. Add water, one teaspoon at a time, stirring to form a dough ball. Wrap dough in plastic wrap and chill 20 to 30 minutes. 

Preheat oven to 350°F.

Roll out dough into a circle that is slightly larger than an 11-inch tart pan. Sprinkle the dough with chopped thyme and roll the herb into the dough surface. Place the dough into the tart pan. Press into bottom and up the sides, cut off any excess dough. Mark bottom of tart with a fork and line with parchment paper. Fill with pie weights and bake 10 minutes.  Remove pie from oven and allow to cool before removing pie weights and paper.

Tomato Tart Filling

While crust is baking, prepare filling.

Melt butter over medium heat in saucepan. Add sliced onion, cover and lower heat.  Cook 10 minutes, stirring occasionally. Stir in the sherry and 1 tablespoon sugar. Cover and cook an additional 10 minutes.  Set caramelized onions aside to cool.

Cut tomatoes in half and place in a bowl. Sprinkle tomatoes with remaining 2 tablespoons sugar; let sit for 2 to 3 minutes and then stir.

Cover the tart bottom with grated cheese, cover cheese with caramelized onions. Using a slotted spoon, let liquid drain from tomatoes, and place on top of onions in a single layer. Sprinkle with a pinch of salt and pepper.

Place assembled tart in warm oven. Bake 25 to 30 minutes. The outer edge of the crust should be a golden color and the tomatoes should have a roasted, cooked look to them.

Cool slightly, then remove the outer rim of the tart pan. Slide tart onto a serving plate and cut into 8 wedges.