Place onions and thyme in a large saucepan over medium heat, drizzle in the olive oil, stir to coat all the onion. Cook stirring for1 0 minutes, or until softened.
Turn the heat down and cook for another 20 minutes. Add the sugar, vinegar and seasoning. Cook for another 20 minutes, stirring every now and then to scrape the sticky bits on the bottom. Take off the heat and use immediately or store in sterilised jars up to a week in the fridge.
Mix the flour, herbs, salt and pepper together in a medium-sized bowl. Cut the butter into cubes and place into the flour mixture, with your fingertips begin to rub the butter into the flour until it begins to crumble and look like breadcrumbs.
Add the ice water and mix until a dough begins to form, turn the dough onto a lightly floured surface and knead until soft. Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.
When you’re ready to use, lightly flour your work surface and rolling pin. Roll the dough out until it’s about 3mm thick, place into tartlet pans and stab the bottom with a fork. Line with baking paper and some beans/rice, place into a preheated oven (220) to blind bake for 10 minutes. Remove the baking paper and beans/rice and bake for a further 10 minutes. Take the tart shells out of the oven and let cool.
Place some caramelised onion into your baked tart shells and top with a slice of goat's cheese, place back into the oven for 10 minutes, until the cheese has melted and slightly golden.