Hello Rain,
If this was not a "friend" then it might be a bit different, that being said, its like what Ed said, what is your value for entertaining ? A romantic dinner for two is an easy 3 hour dinner.
As far as cooking lessons go ? I would tell them to book another night and then give them your 'cooking lessons rates'. For now, ask them to relax at the dining table while you stay in the kitchen and let them enjoy the experience of your graciousness and professionalism.
You may secure clients for future and your friend will respect you for your expertise and the friendly price.
Going private: we are out to make money, true, but future clients , who doens't want that ?
Petals.
ps. right on with Pete. sorry just saw your post.