Cut the plums in half and remove the pits. Toss the plum halves with 1/4 cup of the sugar and let them stand for at least 30 minutes.

Place a 10 inch cast iron skillet (or any heavy-bottomed pan that can be transferred from the stove to the oven) on the stove over medium heat and add the butter.

Once the butter is melted and foamy, add 3/4 cup sugar and cook, swirling the pan regularly, until the caramel is a deep golden color (about six minutes).

Remove the pan from the heat and let the caramel cool in the pan for 20 minutes.

Drain the plums over a bowl, reserving their juices for a future recipe (cocktail?).

Arrange the plum halves, cut side down, in the skillet of caramel, overlapping them slightly in order to pack in as much fruit as possible (they will shrink when cooked). I even cut some in half to fit areas around the outer edge.

Return the pan to the heat and cook over medium-low for 20 minutes without stirring or touching the fruit at all. Let the plums and caramel cool before proceeding to the next step (I let mine sit for an hour).

Preheat the oven to 375 and remove the puff pastry from the freezer.

Allow it to just thaw until you can work with it.

Cut a circle from the puff pastry the size of the top of your skilled and place it over the top of the plums; pinching the outer edge to fit if necessary.

Pierce the pastry a few times with a fork, and brush it with the beaten egg. Sprinkle the remaining two tablespoons of sugar over the top, and bake the tarte for 45-55 minutes, until the pastry is golden and cooked through.

Just before serving, invert the tarte onto a serving platter. The author suggests serving with creme fraiche but I've done it with whipped cream or vanilla ice cream too.