Place a sheet of parchment paper on a bake sheet. Puff pastry comes in two pieces, each folded in thirds. Lay out one piece of puff pastry. Lay two-thirds of the remaining pastry next to the first, forming the pizza. Discard the last third pastry or use for another purpose.
Using a sharp knife, cut a line down each edge of pastry, ~1/2-inch in from the edge, creating a frame. Use a fork and prick holes gently all over the pasty inside the cut "frame" (the point of the cuts and fork pricks is to keep the pastry from rising).
In a medium nonstick saucepan, heat the cream over medium-high heat until reduced by half. Whisk in the Dijon mustard. Remove from the heat.
In a bowl combine the broccoli, sun-dried tomatoes, capers, salt, pepper, cheese, and Dijon-cream. Spread the broccoli mixture over the prepared puff pastry within the "frame" that was cut earlier (this leaves a margin of pastry as a crust around the edge).
Bake at 400F for 25 minutes or until pastry is cooked through. Be sure that the pastry cooks all the way through in the middle of the pizza under the toppings. Yields 4 servings.