Frati offers online reservations at their website:

The prices range from NOK 121 to NOK 245. A popular restaurant in Trondheim, as you can both go for pizza/pasta which is fairly inexpensive, but also go for high quality steaks or excellent fish dishes.

Professional waiters/waitresses and a very well run business. Bari, a bar & cafe, is on the floor below. If Frati is fully booked, try AiSuma (same owners) which is based on the same concept and have a similar menu.