Lots of amber malt and unusual procedures

It can be done! Inspired by the "Giant Ale of Cerne Abbas" recipe in Radical Brewing I decided to make a simple brown ale with a grain bill of half pale malt and half amber malt. The results are far better than I was expecting - this beer got outstanding marks at a blind tasting some friends and I arranged, and I'm thinking of entering it in a competition, though I have no idea under what category.

Lots-of-Amber-Malt Brown Ale

5.5 gallon batch, 120 minute boil

Fermentables:

6 lbs. Maris Otter pale malt
6 lbs. Amber Malt (I used Crisp - these tend to vary a lot.)

Hops:

1 oz. Northdown (8.5% AA) @ 60 mins.
2 oz. Styrian Goldings (5.5% AA) @ 5 mins.

Yeast:

Wyeast 1275 Thames Valley Ale

Unusual Procedure:

Mash for 90 minutes at 152 with 4 gallons of strike water. (Amber malt will convert itself, but it is sloooow.) Collect a gallon of the first runnings and vigorously boil it for 15 minutes. Add this back to mash out. Sparge to collect 6.5 gallons and boil down to 4.5, adjusting hop additions for your boil time. I boil off almost exactly a gallon per hour. Add one gallon of cold water at flame out to get the full batch volume. (And cool quickly!)

OG: 1.060
FG: 1.016
ABV: 6%
IBUs: 35
SRM: 18

Notes:

The theory behind the decoction mash out and the extra long boil was to develop some good caramel flavors without the addition of crystal malt. I have to say, this worked marvelously - I actually like the flavor better than crystal malt and will be experimenting with this procedure on other styles. (Decoction mash out and long boil ESB will be next.)

That looks great, why the long mash and the long boil?

I would try that though looks tasty!

Both are explained in the post. The long mash is because amber malt converts itself really slowly. The long boil was to develop caramel flavors without using crystal malt.

Unless you pulled actual grains from the mash, it's not technically a decoction. Closer to a step mash than anything else. Regardless, that looks like an interesting recipe.

How much of the first runnings do you end up boiling off?
Wouldn't the diastatic power of the marris otter quickly convert the amber malt? Base grains typically have amylases to spare.

Yeah, that's true, I didn't pull grains, but I didn't know what else to call it. I didn't measure the boil off for the first runnings, but I would say less than a quart. I just did that in a big sauce pan on my kitchen stove. Maris Otter actually doesn't have a lot of amylase to spare because it is more highly toasted than other pale malts. If you did this with American two row I think an hour would be fine.