Pork tenderloin with rhubarb, onion and tarragon

Name: Pork tenderloin recipe with rhubarb, onion and tarragon
Yield: Serves 6
Ingredients: 2 x 600g pork tenderloins, trimmed; 50g salted butter; 4 shallots, peeled and cut into wedges; 200g rhubarb, cut into 2cm pieces; 50g caster sugar; 1tbsp whole black peppercorns, crushed; 10 sprigs tarragon