1. Roast your tomatoes with a little bit of olive oil & salt in a 375 degree oven for about 40 minutes. At the same time, caramelize your onions.
2. While your tomatoes are roasting and your onions are caramelizing, boil your potatoes in salted water until tender. Let cool. Slice them by cutting off then ends (and discarding them), then slice the remaining potato into 1/2 inch thick disks.
3. Make your caramel topping. In a small sauce pan over high heat, cook your butter and your sugar together until golden brown. Stir constantly. When it’s finished, pour it on the bottom of your cake pan on top of the parchment paper. Make sure it evenly coats the bottom. Sprinkle the oregano leaves in the caramel.
4. Assemble your tart! Place the potatoes in an even layer at the bottom of the tart pan on top of the caramel. Wedge the tomatoes into the holes between the potatoes. Top with caramelized onions and goat cheese. Place the puff pastry on top and gently tuck the edges down around the potatoes inside the pan.
5. Bake for 25 minutes at 400 degrees and then reduce the heat to 350 degrees and cook for 15 more minutes (or until the pastry is cooked through).
6. Remove from the oven. Within a few minutes, hold a plate firmly on top of the pan and carefully but quickly turn them over together, then lift off the pan.