In a bowl, mix flour and salt. Cut in butter until mixture resembles coarse crumbs. Stir in ice water until dough forms. Wrap in plastic and refrigerate for 30 minutes.

In a skillet, heat olive oil over medium heat. Add sliced onions and cook, stirring occasionally, for about 20 minutes until soft and caramelized. Stir in balsamic vinegar and remove from heat.

Preheat oven to 375°F (190°C). Roll out the chilled dough and fit it into a pie dish. Spread the caramelized onions evenly over the crust.

In a bowl, whisk together eggs, cream, thyme, salt, and pepper. Pour the mixture over the onions and top with crumbled goat cheese.

Bake in preheated oven for 25-30 minutes until set and golden. Let cool slightly before slicing.