Preheat the oven to 375ºF. Prepare a muffin tin with cooking spray.
In a small bowl, rub the sugar and thyme together until fragrant. Set aside.
Slice the plums in half, remove the pits, then slice the plum in very thin slices. Place plums in a microwave safe bowl with the lemon juice and half the thyme sugar. Microwave 30-60 seconds until the plums are pliable. Let cool slightly.
Roll out the puff pastry and cut into 6 strips lengthwise. Warm the apricot jam so it spreads easily. Brush a thin layer over each strip.
Arrange the plum slices, skin side up, overlapping along one edge of each strip. The tops of the plum should extend just beyond the pastry. Fold the bottom of the pastry up and press gently to secure.
Starting at one end, gently roll the strips to form a rose. Place one in each muffin tin. Brush with melted butter. Sprinkle each with the remaining thyme sugar. Bake 35-40 minutes until golden and puffed. Let cool slightly and dust with powdered sugar. Serve and enjoy!