Pre-heat the oven to 200ºC. Lightly oil 2 baking dishes with olive oil. Mix the onions with 1 tablespoon balsamic vinegar and a pinch of salt. In one of the dishes, place the onions, cut side up, and the garlic cloves, and drizzle a little olive oil over them. Separately, mix the tomatoes with 1 teaspoon muscavado sugar and a little olive oil. Distribute them evenly on the other baking dish. Place the 2 baking dishes in the oven – preferably in the middle rack – and roast for 25 minutes, or until the vegetables are golden brown. When they’re done, take them out from the oven and let them cool a bit at room temperature.
In the meantime, prepare the crust: Mix the chesnut and wheat flours in a bowl. Add the salt. Now, slowly pour the olive oil and mix everything with a rubber spatula. Finally, add the water. Using your hands, mix the ingredients together in order to form a ball, being careful not to over mix the dough. If the dough seems too dry and doesn’t hold together, add 1 to 2tablespoons more water.
Place the dough in the lightly oiled tart pan and press it with your fingers, so that the bottom and the sides of the pan are uniformly covered with dough. Now, trim any excess dough. Cover the pan with plastic wrap and refrigerate it while you proceed with the recipe.
For the tofu custard, place all the ingredients for the custard in a food processor, as well as half of the roasted cherry tomatoes (juices included) and the roasted garlic cloves (which you have to unpeel first), and process until totally smooth. Have a taste and adjust the seasonings – adding a bit more tamari and/or a bit more lemon juice – if needed.
Take tart pan out of the refrigerator, cover it with foil and place a few pie weights over it – I used dried beans. Blind bake the crust for 10 to 12 minutes, or until golden brown.
Place the onions in the bottom of the pre-baked tart shell. Fill the latter with the tofu custard and distribute the remaining roasted cherry tomatoes evenly on top. Bake for 25 to 30 minutes, at 180ºC, or until the custard is set and golden brown. Serve with a leafy salad.