Preheat oven to 400° F. Grease a standard muffin tin.
Mix water and lemon juice in a medium bowl. Add apple slices. Microwave for 2 to 3 minutes or until softened. Drain.
Roll out puff pastry sheet on a floured surface to a 12 x 13-inch rectangle. Cut into six 2-inch-wide strips.
Brush 1 strip with sweetened condensed milk mixture. Place apple slices (about 7-9 slices) peel side pointing up, length-wise on the strip, about ¼-inch above the edge of the dough and slightly overlapping.
Beginning on one end, roll the dough to form a rose-shaped pastry. Place in prepared muffin tin and push down gently to ensure it is upright. Repeat with remaining strips of dough. Brush remaining sweetened condensed milk mixture gently over tops of apples.
Bake for 40 to 45 minutes or until pastries are golden. Dust with powdered sugar, if desired.