The tangy, vinegary brown sauce pairs perfectly with breakfast meats, but is scarce in the US
The elements of a full Irish breakfast are as follows: sausage, fried egg, rashers (Irish bacon), mushrooms and/or grilled tomatoes, black pudding, white pudding, and some kind of sliced bread, preferably toasted. You know the drill; you've seen the movies; you might have even eaten the spread at a pub once. But if you started the whole shebang without first securing a generous slab of butter and a brown sauce, then I'm sorry to say, you are doing it wrong. Brown sauce is one of those condiments that's difficult to translate. It's vinegary, tangy, and just a touch fruity, closer to ketchup than barbecue sauce. It's on the Worcestershire sauce to steak sauce continuum, but with a flavor profile all its own: sweet, peppery, just right to cut through the fattiness of breakfast sausage or bacon.
There are a couple different varieties, but the one most clamored-after in my household, thanks to my Irish mother, is YR sauce. YR is short for "Yorkshire Relish," and is the only English-sounding thing that my grandmother allowed in the kitchen. It's a precious condiment, often smuggled back from a visit to my aunts in Dublin and meted out slowly over the course of months. During the month before Christmas, my brothers and I would eagerly anticipate the basket my aunts would mail over full of sausage, rashers, Kerrygold, and YR sauce. On Christmas morning, after frying up the goodies from the basket, we would, at long last, be allowed to used some of the YR sauce.
HP sauce is similar, and even OK, if you can get your hands on it. But YR sauce is scarce on this side of the pond, even in our global economy, or our now post-global economy, or whatever it is. But on this St. Patrick's Day, rather than dying your pancakes green, I urge you to seek out the joy of brown sauce.