Preheat oven to 400F. Defrost pastry sheet by leaving it out at room temperature for 40 minutes or taking it out the night before and defrosting in the refrigerator. On a lightly floured surface, roll the pastry dough out until it is roughly an 8x12 rectangle. Using a very sharp knife lightly score around the edges, about 1/2" in.
Heat a large non-stick frying pan over medium high. Cook the onion slices in the drained marinade from the artichoke until the onion is tender and starts to brown slightly. Set aside.
Remove the rind from the brie (I used goat's milk but any would do), slice the brie and lay it evenly across the tart. Layer the tomato halves on top of the brie. Halve the artichoke hearts and lay them on top of the tomatoes. Finally spread the cooked onion evenly across the top.
Bake for 15 to 20 minutes or until the edges of the pastry turn a light golden brown. Season with fresh cracked black pepper and garnish with basil leaves. Serve immediatly.
Tip: Use a pizza cutter to slice into squares. Cut into smaller pieces for a perfect appetizer.