Put a generous tablespoonful of butter in a saucepan, when it is hot add
half an onion chopped fine, let it stew gently for a few minutes, then
add a pint of canned tomatoes, cook half an hour. Rub a heaping
tablespoonful of flour and one of butter smoothly together and stir into
the tomatoes. Have ready a pint of boiling milk, pour the tomatoes into
a puree sieve with the boiling milk and rub through the sieve. Season
with salt and pepper and a very little sugar. Return to the fire, make
it hot, but be careful not to let it boil, as it will curdle. Serve at
once with croutons.