Paul,
I've made this recipe maybe twice. While I didn't measure, I did want to keep it close to the original so was careful in adding my ingredients. I tinkered a bit until it seemed like I remembered it. I like more flat leaf parsley and a bit more garlic so I went that way. Jalape�o would definitely work for me. You have all that dairy as a cushion, you could probably add a whole minced pepper. Of course, it can depend on the jalape�o itself. My wife and I did dinner and a movie last night and her southwestern burger (Burger Up in Franklin) had sliced fresh jalape�os on it that were scorching. I feel like jalape�os have gotten milder over the years (or my tongue has become as jaded as my general outlook) but these ones were more than Betsy could handle, and she doesn't usually break a sweat with spicy food. Pickled jalape�os would have been perfect.

I always add some kind of heat when making onion dip. Caramelize an absurd amount of onions (without adding salt), then work in some beef "better than bouillon" among other things. That's the base that I'll add sour cream or Greek yogurt to, along with Worcestershire, cayenne, pressed garlic and black pepper. Gonna make a batch to bring to a Super Bowl party in a couple weeks.