Steps
1. Preheat the oven to 375°F (190°C).
2. In a pan, melt the butter over medium heat and add the sliced onions. Cook, stirring occasionally, until the onions are caramelized, about 20-25 minutes.
3. Press the pie crust into a tart pan and prick the bottom with a fork. Bake for 10 minutes.
4. Spread the caramelized onions over the partially baked crust, top with crumbled goat cheese, salt, and pepper.
5. Bake the tart for another 15-20 minutes, or until the crust is golden and the cheese is melted.
6. Garnish with fresh thyme leaves before serving.