Lay puff pastry flat onto a cutting board. Place a 9-inch baking pan on top, and gently use a sharp knife to cut out a circle, using the outside of the pan as a guide. Use a fork to poke holes throughout the dough for ventilation. Set aside.
Peel, core, and cut the apples into wedges.
Preheat oven to 375°F.
In a large saucepan over medium heat, add the water and sugar. Gently stir continuously and cook until the mixture starts turning color, about 5-7 minutes. Once the mixture turns a light amber color, add the butter. Continue stirring until the color turns into a light brown (see Step by Step section for photo example). Add the apples to the saucepan and gently toss to coat them.
Cook the apples in the caramel for about 15-20 minutes, turning the apples regularly to evenly coat all sides. When the caramel is reduced enough that the apples have soaked up most of the caramel, remove the pan from heat.
Arrange the apple slices in into a circular pattern on the bottom of the cake pan. Press the apples tightly together. Note: in the photos, you'll see how much the apples move apart during baking. I usually put more apples (about 8 instead of 6) now than I did during these photos(. Pour any remaining caramel over the top.
Place the puff pastry circle on top of the caramelized apples.
Bake uncovered at 375°F for 45-50 minutes, until the pastry is golden brown and firm. Allow the tart to cool at room temperature for 45 minutes to 1 hour, then flip it over and invert it onto a plate. The caramelized apple side should now be face up.
Notes
Makes approximately 4-6 servings. Notes:
Give yourself time to make the caramel. Caramel is so simple yet can be very tricky to make. Watch the sugar and water carefully to ensure the sugar doesn't crystalize and the caramel doesn't burn. If the sugar does start to crystalize, there is nothing you can do to save it, you just need to start over.
Be sure to wear oven mitts when flipping over the tarte onto the plate. Even though it has slightly cooled, the pan may still be hot.