For the tart
Place the puff pastry sheet on a lightly buttered tart shell with low sides. Line the sheet with parchment paper and fill with dried beans. Bake in a preheated oven at 180⁰C until very light golden brown, about 15 minutes. Remove the beans and cook until the dough develops a nice golden brown color all over and has turned crispy. Cool completely. Heat a sauté pan over medium heat, add the butter and sweat the bacon until slightly crispy. Add the garlic and green onions and cook for 1-2 minutes until a nice aroma develops. Mix the smashed potatoes with the thyme and parmesan and season with salt and pepper. Place this mixture in the prebaked tart shell in an even layer. Spread the bacon mixture evenly over the potatoes and top with the asparagus. Bake in a preheated oven at 180⁰C until the top of the tart gets golden brown, about 15 minutes. Let the tarts rest for 20 minutes before cutting in pieces. Serve hot, warm or at room temperature.