Preheat the oven to 220°C.
Very thinly slice the potatoes (a mandolin is good to use here).
Put into a bowl with the garlic, thyme leaves and olive oil, season generously with salt and pepper and mix well.
On two baking paper lined trays, put a sheet of pastry. Score a line 1cm around the edge and prick inside all over with a fork.
Divide the potato mix over the two bases in a single layer, keeping the edges clear.
Put into the oven and bake for 20 minutes.
Remove from the oven and add the cheese evenly over the two tarts and return to the oven for 3-4 minutes.
Sit for a few minutes before slicing.