I know this is an old thread, but I thought I'd add a few observations on espresso. I've been a coffee roaster for 20 + years now and can tell you, like with most things in life, garbage in, garbage out. Starbucks would be a poor choice for any recipe, but more so for a recipe that you want to avoid bitterness. The compounds in coffee will tend to taste more and more bitter the more they're extracted. The extraction and degradation of those compounds is going to happen while it's being heated in a saucepan.
I might give this recipe a try at some point today, I need to check but I think I have most of the ingredients on hand. But if you're trying to avoid bitterness, and don't have a good espresso machine/grinder at home, then you can easily substitute a very strong brew ratio of a coffee that isn't roasted into oblivion. Basically, use any bean that isn't shiny with oils. You'd be surprised at some of the flavors you can get out of a good coffee bean. I've made several sauces over the years that use strong coffee and or espresso and generally you're not going to find a strong coffee flavor in the mix, there's just more maillard compounds in the mix the give you almost a gravy like complexity.
I'll wrap it up with a Aaron Franklin encounter I had here in San Francisco last year. He was in town to promote his cookbook, and had a pre-sold (sold out in 3 seconds) dinner party at 4505 Meats. My dad was in town and I took him around the city to see the sights. My fiancee wanted to see the Li Po Lounge since it's a "world famous" dive bar that has really highly rated Mai-Tai's. So we're there, sitting at the bar, sipping Mai-Tai's and in walks Aaron completely randomly. My dad acted like he was meeting the President, being that he's also a competitive BBQ'er and judge.
Aaron's a super down to earth guy and when the conversation we had turned towards coffee, he was interested in hearing my recommendations for the city. Apparently he's got a 3 group espresso machine in his restaurant to keep his staff and himself well buzzed for the early morning work of manning the pit.
Since long posts without pictures suck, here's my dad and Aaron at the Li Po Lounge