How to Make It
Preheat oven to 400°F. Place the puff pastry sheet on a baking sheet; prick evenly with a fork. Bake in oven for 15 minutes; remove pan to a wire rack.
Combine the rhubarb, fennel, sugar, salt, and pepper in a medium bowl.
Spread the cream cheese evenly over the pastry, leaving a 1-inch border. Top with the rhubarb mixture. Return pan to oven and bake until the pastry is golden brown, 12 to 15 minutes. Sprinkle with the thyme. Cut into 4 pieces.