In a mixing bowl, combine flour and salt. Cut in the cold butter until the mixture resembles coarse crumbs. Stir in ice water, a tablespoon at a time, until the dough comes together. Shape into a disk, wrap in plastic, and refrigerate for 30 minutes.

In a skillet, heat olive oil over medium heat. Add sliced red onions and cook, stirring occasionally, for about 20 minutes until they are soft and caramelized. Remove from heat and let cool slightly.

Preheat the oven to 375°F (190°C). Roll out the chilled dough on a floured surface and fit it into a pie dish. In a bowl, whisk together eggs, heavy cream, thyme, salt, and pepper. Stir in the caramelized onions and goat cheese. Pour the mixture into the crust.

Bake in the preheated oven for 25-30 minutes, or until the filling is set and the crust is golden brown. Let cool for a few minutes before slicing.