Method
First, make the pastry; put the flours, salt and butter in a food processor and pulse until they form coarse ‘breadcrumbs’. Add the water a tablespoon at a time and pulse again until the dough comes together (you may not need all the water, or you may need a little more). Tip the dough on to a floured work surface and shape it into a ball, then flatten it into a thick disk, wrap it in cling film and refrigerate for at least 30 minutes. When the 30 mins is nearly up, preheat the oven to 190⁰C (Gas Mark 5). Lightly re-flour your work surface and rolling pin, and line a baking sheet with baking parchment, then tip the dough on to the surface and roll it out to roughly the size and shape of a large dinner plate. Lift the dough on to the lined baking sheet. Next, spread an even layer of mustard (or tapenade, or chilli jam) on to the pastry, leaving a 5cm border all around the edge. Cover this with a thick layer of ricotta, then lay the tomato slices on top and sprinkle them with the chopped garlic and the thyme leaves. Gently fold the edges of the dough up and over the filling, working your way around the galette and overlapping the dough as necessary. Press gently to seal the edges, then brush them with the beaten egg and put the tray into the preheated oven. Bake for about 40 minutes, or until the crust is golden and the tomatoes are cooked through.