Remove the legs and wings from the grouse, retaining the meat for the sausage, and the bones and trimmings for the grouse sauce.
Brown the butter and add the lemon juice. Add the aromatics and leave to cool a little. Smother the birds in the aromatic butter and place in a sous vide bag. Compress and poach in a water bath at 52°C for 45 minutes. Remove from the bag and remove the breasts