1. To make the tart dough, cut the butter into small pieces and work it into the flour with your fingers. Add the salt and quickly gather the dough together. Cover and refrigerate for about 30 minutes. Set aside approx. 50 g of dough for decoration, then press the remainder into two greased loose-base tart pans (approx. 15 cm in diameter). Press the dough all the way up the sides. Prick the crusts and pre-bake in the middle of the oven for approx. 12 min. at 200°C (conventional oven).
2. For the filling, place the drained fetta in a bowl and mash slightly with a fork. Add the eggs, lemon juice, thyme, salt and pepper and whisk until combined. Stir the finely grated beetroot into the egg mixture. Pour the mixture into the tart crusts. Roll out the rest of the dough on a floured surface. Cut out hearts with a cookie cutter or a knife. Arrange the hearts on the tarts. Finish baking the tarts in the middle of the oven for approx. 35 min. at 200°C (conventional oven).
3. To make the quick-pickled beetroot, place water, lemon juice, sugar and peppercorns in a saucepan and bring to a boil. Add the beetroot and cook for about 15 min. over a low heat and uncovered. Drain the beetroot and leave them to steam off in a colander until serving.
4. Serve the warm tarts with a mixed green salad and the quick-pickled beetroot.