How many people does this serve? Should I quadruple for four portions? Thanks!

Technically and in some old recipes, "chicken breast" refers to that part of the chicken on both sides of the breast bone - like a turkey breast, when you're buying parts for a small Thanksgiving dinner instead of a whole bird.

In most modern recipes and food writing, however, "chicken breast" refers to that part of the chicken from only one side of the bone, and average size sold in USA groceries is 6 oz. or about 180g.

So, assuming the recipe was written for that one-side-of-the-breast-bone cut (and not Lori's pterodactyl size ones), yes quadruple the original to serve a dinner party of 4.

Also as Lori suggests, it can't hurt to cook more for the fridge and home use later in the week. And/or accommodate big appetites at your dinner.

The recipe says it produces one portion- although I suppose that depends on the size of the chicken breast and how hungry the consumer is. Stores where I live seem to get chicken breasts off pterodactyls, so they are large enough for two hungry adults once flattened out. I might use two of them and increase the sauce ingredients by four, if it were me. So for that you would have to gauge based on the size of the chicken breasts you get. The sauce I would increase according to the number of servings. I doubt anyone would complain if you did simply increase the recipe fourfold though, ang at least that would make plenty for everyone to enjoy. Cooked leftover chicken is a useful thing in the frig as well.