Butter a 10-cup (2.5 liter) soufflé
dish well. Sprinkle in about 2 tbsp (30ml) sugar and shake it around
to coat bottom and sides. Make a collar of doubled aluminum foil
that will just fit around the top of the dish. Butter it and
sprinkle with sugar. Fasten it tightly around the soufflé dish,
sugared side in. Put chocolate and butter in a small bowl and set in
pan of simmering water to melt. Combine flour, sugar and salt in
large heavy saucepan. Stir in milk gradually. Set over moderate heat
and cook until mixture is very thick and beginning to bubble,
stirring constantly. Remove from heat.
Beat egg yolks well with a wooden spoon.
Beat in a little of the hot mixture. Gradually stir egg yolk mixture into
mixture in saucepan. Cook just until mixture bubbles, stirring. Remove
from heat. Add chocolate mixture and vanilla and beat to blend well. Cool
10 minutes. Heat oven to 350F (175C). Combine egg whites and cream of
tartar in a large mixer bowl. Beat until egg whites are stiff but not dry.
Add about 1/3 of the egg whites to the chocolate mixture and fold to blend
very well. Add remaining egg whites and fold as little as possible just
until blended. Pour into prepared soufflé dish. Bake 55-60 minutes or
until just set. Serve immediately with
Liqueur Sauce spooned over.