Melt butter and stir in flour.
Gradually add milk and cream, stirring constantly.
Cook over low heat, stirring all the time, until sauce is thick and smooth.
Stir in salt and pepper and fold in whipped cream.
While making the sauce, cook trimmed cauliflower whole in boiling salted water until tender.
Drain; place on hot plate and keep hot.
Add chopped shrimps to sauce and heat thoroughly.
Pour sauce over cauliflower and decorate with whole shrimps.