Step 1In a food processor, process the flour, salt and butter for about 5 to 8 seconds, so that some pieces of butter are left. Combine half of the egg yolk (saving the other half for the filling; set aside in the refrigerator) with one-fourth cup cold water and drizzle through the tube of the food processor while pulsing. Pulse until the dough forms a ball and pulls away from the sides.
Step 2Alternatively, the dough can be mixed by hand. Put the flour and salt in a bowl, cut the butter into pieces and work it into the flour with your fingertips. Make a well in the middle of the flour and butter mixture and add the half egg yolk and one-quarter cup ice water. Stir quickly with a fork to start bringing the dry and wet ingredients together. When the fork can't do any more, use your hands just to bring the dough together. Don't knead or press -- all you have to do is gather up the dry parts as quickly as possible. If your hands get too warm, put them under cold water for a few minutes.
Step 3Wrap the dough in plastic wrap and chill in the refrigerator for at least 30 minutes, or up to 8 hours.
Step 4Heat the oven to 350 degrees. Take the dough out of the refrigerator. Dust your work surface and rolling pin with flour and roll out the dough, lifting and turning it all the time so that it does not stick to the surface. Roll the dough out into a square about one-eighth-inch thick. Roll the dough around the rolling pin and gently lift it into the tart pan, gently pressing the dough into the bottom of the pan and up against the sides. Trim the edges. Chill again for about 30 minutes.
Step 5Line the tart shell with parchment or foil and fill it with pie weights or beans and bake for 15 minutes. Remove the weights and the parchment or foil and prick the crust with a fork. Continue baking an additional 20 to 25 minutes until golden. Cool the tart shell on a rack.
Step 1Heat the oven to 350 degrees. Line a baking sheet with foil, place a rack in the baking sheet and roast the tomatoes skin-side up for about 2 hours, until the liquid has gone and the skins can be removed easily. Season the skinned tomatoes generously with salt and pepper and drizzle a little oil over them. Allow to cool to room temperature.
Step 2In a mixing bowl, beat the half and half, eggs, egg yolk, one-fourth teaspoon salt and one-eighth teaspoon pepper and nutmeg until they are well mixed.
Step 3Place the tart shell on a baking sheet and scatter the cheddar cheese over the base of the tart. Place the tomatoes on top of this and spoonfuls of ricotta in between the tomatoes.
Step 4Pour in as much of the cream mixture as you can without it spilling over the top; you may have some cream mixture left over. Sprinkle with the thyme.
Step 5Transfer carefully to the oven and bake for about 30 to 40 minutes until the filling has set and is lightly golden. Allow to cool slightly before serving.