Preheat oven to 400 degrees Fahrenheit. Line a cookie sheet with parchment.
Roll out the puff pastry shells until they're about 4 inches in diameter. (The purpose of this is to create a larger surface area for your big heirloom tomato slices!)
Bake per package instructions. Mine took about 20-25 minutes. Remove from tray and cool slightly before assembling.
Press down the center of the puff pastry shells with the back of a spoon. Into the cavity spread about 1/6th of the boursin cheese.
Layer 2 tomato slices on top of each puff pastry. Sprinkle with coarse salt and freshly cracked pepper, to taste.