Mix a roux by melting the butter and whisking the flour to form a smooth paste. Gradually add the liquid from the tin of asparagus.
Once the flour is cooked (when the sauce coats the side of the pan) add the asparagus pieces.
Lay the vol-au-vents on a baking tray. Using a teaspoon, fill the pastry cases with the asparagus mixture and place in a moderate oven for 10-15 mins or until well heated, without burning!
Bit tast less. Will add garlic next time.
it's called a vol-au-vent, not a vol-a-vent