2 large onions (about 1 1/2 lbs.) sliced thinly
2 tbsp olive oil
1/2 lb. Gruyere cheese shredded (about 2 cups)
1/2 lb. plum tomatoes cut into 1/2 inch wedges
1/2 lb. medium yellow tomatoes (or 1/2 lb. plum tomatoes if yellow tomatoes are not available) cut into 1/2 inch wedges
1/4 cup Nicoise olives, pitted
One pie crust (I used the Pillsbury prepared pie crust dough from the refrigerated section in the grocery and it worked just as well)
In a large heavy skillet cook onions with salt to taste in oil, covered over moderate heat, stirring occasionally, until softened, about 20 minutes (I added 1 tbsp fresh thyme leaves and it was amazing). Remove lid and cook onions, stirring occasionally, until golden and any liquid evaporates. Remove skillet from heat and cool onions slightly.
Precook pie dough in a 12 inch tart pan or quiche dish according to package instructions and when done allow to cool. Preheat oven to 375 degrees for the tart. Spread onion mixture over dough and top with cheese. Arrange tomato wedges and olives in concentric circles and season with salt and pepper.
Bake taRt in middle of oven 1 hour or until it looks like the tart is “set”. Cool on a rack. Remove rim if using a tart pan and cut into wedges. Serve tart warm or at room temperature.