Combine the salt, pepper, bay leaf, thyme and flour and rub into the liver.
Heat the butter and saute the liver and onions over moderately high heat until liver is brown.
Add the wine and sugar.
Reduce heat, cover and simmer slowly for 1 hour.
Slice the liver and arrange on a warm servitjig dish.
Cook the liquid over high heat until reduced by half.
Strain and pour over the sliced liver.