Position a rack in the center of the oven and heat the oven to 450 degrees F.

Thinly slice the cheese and then crumble and tear it into a small bowl. If the cheese has a rind, make sure it's torn into small pieces. Add the cream and mash together with a fork until combined.

Roll the puff pastry on a lightly floured work surface into a 12x17-inch rectangle. Use a pizza cutter or sharp knife to cut the pastry in half lengthwise and then cut a 3/4-inch strip off all 4 edges of each piece of pastry. Transfer the two large pieces of pastry to a 13x18-inch rimmed baking sheet. Dip a pastry brush in water and brush a 3/4-inch border around each large piece of pastry. Stack the trimmed strips of pastry onto the damp dough, creating a border all the way around.

Dollop and spread the cheese mixture inside the borders of each pastry. Evenly grate the zest of the lemon over the cheese. Scatter the rosemary leaves and grind a little pepper evenly over the top. Bake the tarts until puffed and deep golden brown on the top and golden on the bottom, about 17 minutes, rotating the pan half way through baking. Cut each tart into 3 or 4 pieces and serve hot.