Begin by making the pastry. Place the flour and butter in a food processor and process until the mixture resembles bread crumbs. Add the egg yolk, herbs and water and pulse until the mixture begins to come together to form a ball. Turn the mixture out onto plastic wrap and shape into a disc. Refrigerate for 30 minutes.
Remove the pastry from the refrigerator and roll out the pastry on a lightly floured bench or silicone baking mat until approximately 5mm thick. Line 8 mini loose bottomed tart tins with the pastry, making sure to press into the sides, and trim the excess. Refrigerate for 15 minutes.
Preheat the oven to 180 celsius (355 Fahrenheit) and line the tart with baking paper and fill with baking weights or beans. Bake for 10 minutes before removing the baking paper and weights and baking for a further 5 minutes or until the base is dry and lightly golden. Set aside to cool.
Place beetroot in a saucepan of cold water and bring to the boil. Reduce heat to medium-low and simmer for 1 hour or until the beetroot is tender. Drain the beetroot and run under cold water and leave to cool before grating.
Heat the butter and oil in a frypan over medium heat. Add the onions and cook, stirring occasionally, until the onions are softened. Add the apple, beetroot, vinegar and cook, stirring, for 5 minutes. Spread beetroot mixture over the bottom of the tart bases. Crumble the goat cheese over the beetroot filling.
Whisk the egg and yoghurt together and carefully pour over the beetroot filling. Sprinkle the dill over the top and bake for 10 minutes or until set.
Recipe by Delicieux at http://www.ledelicieux.com/recipes/beetroot-and-goats-cheese-tarts/