Melt butter in a medium saucepan, add bacon and onions then fry for two minutes. Add the flour and KEEN’S mustard powder and mix well with a wooden spoon for 1 minute. Add milk slowly and continue to stir until thickened.
Add diced fish fillets and tarragon into the sauce. Pour into an ovenproof dish. Top the dish with puff pastry, allow for shrinkage by having some extra overhanging. Cut a small cross in the centre of the pastry, brush with a little bit of excess milk.
Bake in oven for approximately 20 minutes, or until pastry is golden and fish is cooked through.
Serving suggestion: Serve with steamed vegetables or a fresh garden salad.
Recipe Tip
Serving suggestion: Serve with steamed vegetables or a fresh garden salad.