Mix flour with salt and rosemary. Cut the butter into small pieces. Make a well in the flour and add the egg and butter. Working quickly, using your hands, combine all the ingredients and knead briefly into a smooth ball. Wrap in plastic wrap and refrigerate for 30 minutes.
Preheat oven to 180°C (approximately 350°F).
Put dough on a floured surface and roll out thinly to about 0.4 cm (approximately 1/4 inch). Cut out biscuits using a flower-shaped cookie cutter about 5 cm (approximately 2 inches) in diameter. Place biscuits on a parchment-lined baking sheet and bake for 10-12 minutes. Remove and allow to cool.
To serve, stack, and garnish with a dollop of crème fraîche if desired.