Preheat the oven to a low heat, around 250° F / 120° C. Line a baking with parchment paper.
Bring a small 1-quart pan of water to boil on the stove. Cut an "x" into the bottom of each tomato. Drop into the boiling water for 5 to 10 seconds. Carefully remove with a smooth. Tear the flaps at the "x" to remove the skin. Cut out the core, cut into quarters and remove the seeds. Repeat for the other tomatoes. Put the slivers of tomato onto the prepared baking sheet. Drizzle with olive oil, add the peeled garlic, thyme and salt. Gently bake for about 45 minutes until the slivers soften.
In a large sauté pan melt the butter with the olive oil. Add the onions and bay leaf. Cook and stir patiently until they’re brown and soft, about a half hour or so. Once browned, sprinkle with flour and a dash of salt and cook another 2 minutes. Set aside to cool.
Once the tomatoes are softened, increase oven to 425° F / 220°C.
Roll out the dough, press it into a quiche or pie pan. Pierce the bottom with a fork. To keep its shape, set parchment or aluminum foil in the center and fill with pie weights or dry beans. Bake for 5 minutes. Remove weights, brush the pastry with beaten egg and return to oven for 7 minutes. Cool slightly.
Meanwhile, whisk the eggs and cream in a bowl. Stir in about one-third of the cheese, salt, pepper and thyme. Stir in the cooled onions and then pour into the pastry shell. Arrange tomatoes in decorative pattern on top. Sprinkle on remaining Gruyère. Bake for 25 to 35 minutes until firm, slightly browned and a bit puffy.