I seldom brew strong bitters. When I do, I always remind myself to never go above 5% on the C-malt, it just clutters up the beer and makes it a drag to choke down. I'm a lot happier at 2.5% on my UK ales that don't have dark roasted malts drying out all that C-malt body. Less C-malt makes for a much more guzzle-able beer--which is what UK beers are designed to be.
My advice:
1) Use a milder tasting UK pale ale malt to establish the grist. I really like Warminster Otter in this role. Writing from the US, the Simpsons and Crisp Otter that we get really needs a bit of adjunct dilution once the gravity passes 1.045. They're both *very* full-throated malts. If you can't get Warminster, Golden Promise is a good alternative, it's very flavorful but won't overbearingly dominate the grist. If you can only get Crisp or Simpsons, just substitute a pound, maybe 1.5lbs, of US 2row. That'll take the edge off, without compromising their contribution.
You might be tempted to toss in some Amber malt, but trust your UK base malt. It has more than enough flavor. Leave your amber malt for darker ales.
2) Don't be creative. A good UK pale malt, UK hops, and a flavorful UK yeast like Pub, '69, or WY1468 will get you where you want to be--once you've established that, you can start messing around on your second batch. I would avoid most other strains (unless you're a degenerate and you like Ringwood) because they're all kinda lifeless with homebrew techniques.
Also, no, 85 IBU isn't going to make your ESB amazing, we've already tried that. It sucks. Balance is your friend. Once you've found that, then you can explore a bit. An ounce of EKGs at 60, 1oz at 20, and an ounce at 5-KO is pushing it close to redline. A half ounce of keg hops is plenty, a quarter ounce will get the job done. I used to use a smaller charge of Target or Challenger at 60, but I prefer a larger charge of EKGs/Fuggles/etc. I can't prove this, but I think a larger 60min charge makes for a better beer.
2a) UK hops in the US are really hit or miss. Good EKGs are amazing, but hard to come by. You might want to use Willamette hops instead. They're actually Fuggles descendants, but are often much better than the passed-over-and-passed-over-and-passed over by UK buyers tripe that we get in the US. If you go the US route, pay attention to your AA's, US hops tend to throw down a few more IBUs.
3) Corn, yes corn. I would suggest using .5-1lb of flaked corn. In larger UK ales it provides a very subtle, very thin sweetness that isn't particularly sweet until you find it within the beer, then you really appreciate it. Its primary role, though, is to make the beer light on the tongue and quaffable. It keeps it from being too heavy while leaving that amazing lingering corn sweetness. If I'm brewing a light colored UK ale above 1.045, usually I'm using corn. You know how the Belgians use sugar to boost gravity without making it cloying? It's like that. Given how flavorful most UK malts are, once you get above 1.050, they need a bit of dilution to keep them light on the tongue. Corn is great at doing that.
4) So color... We taste with the eye as much as with the tongue, so this *is* important. In the past, I used to use Sinamar. Unfortunately, it's hard to come by these days and very expensive. As such, I now like to use .5-1oz of Midnight Wheat in this role--it's cheap and it does the job! It's very flavor neutral in those quantities. Also, remember, that the UK bottled beers that we get over here are badly damaged by travel. They're a lot darker and a lot flubbier than they are in the UK. You only need a hint of coloring, just like the UK brewers do with their caramel coloring.
5) Invert sugar, in my opinion, is the key tool in UK ales. Contemporary UK brewers seem to be hardnosed in their rejection of adjuncts in much the same way that US brewers were back in the 80's and 90's. As a US brewer, I think it's adorable to see our UK brethren throwing their little tantrum. Joking aside, invert sugars provide a lot of the flavor that crystal malts add to a beer, but they're fermentable so they don't leave that horrible, cloying body behind. I like to use them because you get to add flavor without paying the heavy body tax. Again, think like a Belgian-- max flavor and max lightness. Yeah, an ESB is substantially bigger than run of the mill bitters, but that doesn't mean it has to be a slog to drink. The whole point of the bitter style is drinkability, right? If you want a fat sipper, brew a Burton Ale, an October Beer, or a Wee Heavy. Use sugar in your ESB to keep it slammable.
As mentioned above, I don't brew many ESBs, so I've never used invert sugars in an ESB recipe. That said, I'd say 1lb of invert #2 would do you a lot of good, a 1/2lb of invert #3 would provide a touch of color and some background flavor depth. If you go that route, delete the corn I mentioned.
6) Finally, C-malts. Use one from the UK and use the smallest amount possible. You want an ESB to be rich and full, yet drinkable. To me this suggest a darker C-malt in a small quantity. I mostly use UK 50/60 in my UK ales, for ESB, I prefer UK 60/70 and I prefer to keep it around 2.5%. The less used the better.
7) When you mash, remember it's a big beer. Mash low. I brew a lot of tiny UK beers and I seldom mash above 152F. UK malts were designed for UK beers. They'll give you all the body you need if you brew them with standard techniques. There's no need to mash them at 158F--unless you want them to taste like they have too much C-malt.
8) For the love of the Great Pumpkin, don't Burtonize your water. Just don't. Seventy calcium, 100 sulfate, and less than 100 chloride should get the job done. I like to keep my pH on the high side throughout the brew day because UK ale yeast aggressively lower the finished ale's pH, typically around 3.9-4.0. They can get a bit tart, if you let them, so I like to elevate my pH a bit.
9) If you want a big fat slob of a US ESB, go with two row to 1.055, then add 1-1.5lbs of C-120, and hop it with Mt. Hood and Willamette like you're all outa F's to give. Sing Rule, Britannia! while kegging it to make it extra special good. If you had to google Rule, Britannia! stop what you're doing and call it a red IPA because people like you deserve to drink red IPAs. If that makes you feel sad, just don't do anything that I've described in this paragraph and you should be okay.
Well, that's some of the stuff that I know.
I hope this was useful to you.
) and brew with confidence.
