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
6 lbs. Maris Otter pale malt
6 lbs. Amber Malt (I used Crisp - these tend to vary a lot.)
1 oz. Northdown (8.5% AA) @ 60 mins.
2 oz. Styrian Goldings (5.5% AA) @ 5 mins.
Wyeast 1275 Thames Valley Ale
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!)
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.)
Beauty is in the eye of the beer holder.