Preheat oven to Gas 4-5, 180°C, 350°F. Roll out pastry and divide into four squares (17cm x 17cm), then cut in half to make two triangles of large enough size to wrap cutlets.
Take lamb cutlet, place into pastry triangle. Place half teaspoon of mint jelly onto each cutlet followed by a large sprig of rosemary. Wet edges with water and fold pastry around cutlet to encase (leaving bone sticking out).
Brush with egg and milk glaze. Place on a non-stick baking sheet and bake for about 20 minutes until pastry is golden brown. Mix together mint jelly and cranberry to make a dip.
Serve lamb cutlet en croûte as a canapé, snack or main course