This is a variation on your basic pan-seared steak. It's a little lower-fat than your usual steak frites, since there's no need to mount the sauce with butter (it's quite nice on its own). It is sort of English-food-inspired-without-actually-being-English so it goes very nicely with things like mashed potatoes and basmati rice.
The Guinness flavor actually stays in the background as a subtle bitterness; it sets a background for the tomato paste and the (rather lingering) shiitake flavor. You might want to serve a lighter beer or wine with it than the stuff it's made with, though; what is subtle on the steak will be noticeably bitter when you soak it up with the bread, so choose your accompaniments appropriately.
1.5 lbs/750g boneless steak (NY strip or shell sirloin)
12 oz/355 mL Draught Guinness
1 medium onion, half chopped, half sliced
6-8 shiitake mushrooms, sliced, stems removed, plus one reserved whole
2 tbsp tomato paste
pinch dill
butter
salt and pepper to taste
In a small saucepan over medium high heat, bring Guinness to a simmer and whisk in tomato paste. Reduce heat to low and add dill, a pinch of salt, whole mushroom and sliced onion; let reduce by about 1/4.
Preheat a heavy skillet (cast iron is fine) over medium-high heat. Cut steak into serving pieces and salt lightly with kosher salt.
Melt 1-2 tbsp butter in skillet and add steak. Sear as you normally would a pan steak; don't cook it over medium unless you have special requests.
Remove the steak to the side to rest and add chopped onion and sliced mushrooms; saute in pan drippings (adding more butter only if absolutely necessary) for about a minute until onions start to become translucent, then add Guinness reduction and deglaze. Remove from heat and allow to reduce until sauce is thickened; you may return any juices exuded from the resting steak to the pan if you wish. Correct for seasoning, but note that mounting the sauce with butter is very optional and probably unnecessary.
Serve steak with sauce and a generous amount of onions and mushrooms on top.
Variations
Some people don't like mushrooms, and shiitakes in particular have a very lingering flavor that might be a little bewildering to someone used to the less puncy white mushrooms. You may want to add a little bit of garlic (not more than a clove or so) to round out the flavor, or substitute chicken broth for 1/3 of the Guinness.
