Firstly, make the shortcrust pastry as this will need to rest in the fridge for at least 30 minutes. Rub the butter into the flour to create a breadcrumb consistency. Add the water, a little at a time, to achieve the correct consistency. Wrap in Clingfilm and leave in the fridge to rest.
Sweat the onions in a pan with the sugar, thyme and 1 teaspoon of balsamic vinegar. Finally, season to taste and when the onions have softened, remove from the heat and allow to cool.
To prep the kohlrabi, you need to wash the outside removing any dirt. Cut off the top and bottom removing 1 cm to give you a sturdy base when removing the rest of the skin. Cut the thick green skin off using a knife. Cut into the desired shape, either wedges or squares.
Steam the kohlrabi by either using a steamer or add around 2.5cm of water in a saucepan and set up a collapsible steamer inside. Bring the water to the boil, and place the kohlrabi inside. Steam for 5 minutes until the kohlrabi is soft and tender. Set aside.
In a saucepan add 250ml balsamic vinegar, add sugar to taste and reduce until the consistency coats the back of the spoon.
Line small tart cases with your pastry that has been resting and blind bake for 15 minutes. Remove from the oven and fill with your softened onions. Top with rough chunks of goat’s cheese and bake in the oven for 5-10 minutes.
In a bowl combine the salad leaves with the kohlrabi, dress with olive oil, salt and pepper. Assemble on a plate and drizzle over your balsamic reduction when the tart is ready to serve.