Adding Calories

What do you suggest for adding some calories and putting weight on a pug?
Mac is too skinny at 14lbs, even the vet said so, and suggested I put some weight on him.

I know I could just increase his food, but what else would do the trick?
A dab of peanut butter on the side of his dish with each meal? Nutrical?

I would add in some protein. Raw or cooked meat, or canned fish, or fried egg or cottage cheese or greek yogurt. Something high is in protein will increase calories and be good for him.

My Ichiro has weight fluctuation issues too. I usually increase his THK a bit and add in more meat.

Peanut butter as a treat would be good too. We did that when Ichiro lost too much weight. He got one spoon of peanut butter per day for about 2 weeks.