We went to Leo & Mas as we were staying at the Banthai and it's right out the front of the hotel.
The restaurant is decorated superbly with the standout being the shelves of coloured pasta they looked great and I want their cat sculptures ;-).
The wait staff are terrific very professional and accommodating and you only need to look like you need something and they will be there, also the girls always wear heels to die for.
The menu is traditional Italian cuisine from pasta dishes to some great seafood dishes with an extensive wine list to compliment the food and the desserts were just too good to resist.
They also have a pizza oven out the front which is also available for take always if you want a night in your room.
Overall one of the best restaurants we have been to and not just in Thailand.