Have you tried a smaller diameter pot?

I was having the same problem (the bread still tasted great, but didn't look very pretty), so I tried multiplying the recipe by 1 1/2, thinking that my pot might be too big--sure enough, the larger loaf turned out beautifully rounded! I may even try doubling the recipe next time.

A couple of the likelier possibilities:

-Your oven might be too hot, which would make the crust form too fast, which would mean the dough doesn't have a chance to expand in the oven.

-It's no-knead dough, which means you aren't kneading, which means you aren't developing the gluten in the wheat. Gluten development is what makes the bread able to hold the CO2 gas as the dough rises.

-

What type of flour are you using? If you're in the south, are you getting a flour more suited to biscuits & cakes?

Are you using unbleached flour? The unbleached flour is higher in protein resulting in better gluten development. You may also want to consider adding vital wheat gluten. I'd suggest checking out the Artisan Bread in Five Minutes a Day books or at least their website, www.artisanbreadinfive.com.

Thanks for the tips!

I noticed just last week that my oven indeed runs a little high, by about 25F, so I'll definitely have to have a re-do in a cooler oven and in a smaller pot!

I've been using Trader Joe's unbleached all-purpose flour, sometimes subbing 1 cup with Trader Joe's whole-wheat flour - I prefer the taste of whole-wheat.

Interestingly enough, I've been using the Minimalist recipe from NYT http://www.nytimes.com/2006/11/08/dining/081mrex.html?scp=1&sq=no-knead&st=cse, which calls for a 1/2tsp less yeast than the Kitchn recipe, but I've been letting it sit out for over 12 hours... Have to try the Kitchn recipe to see if my flat patties can be transformed!

I second the new yeast - my sister was so discouraged after baking several batches of different things that were on the flat side...her yeast wasn't expired or anything, but buying a new jar solved the problem.

Try proofing your yeast first to see if that's the problem.

i think sometimes my bread turns out flat because i let it rise TOO long : it deflates or something (although this is a totally non-scientific guess)

i'm curious about the commenter who doubled the recipe: what size pot do you use?

google the recipe for Cook's Illustrated "almost no-knead bread." They add a few ingredients (beer and vinegar) to the Bittman/Lahey formula and the bread is infinitely more flavorful--and shapely, because you knead it 10-15 times after the first rise and then tuck the edges under to form a ball with some structure to it during the second rise. I think it is also a bit less hydrated than the Bittman one, so it doesn't spread out as much and will hold a shape.

I am also a fan of the parchment paper "sling" to transport the risen loaf to the hot cocotte, so that it doesn't deflate upon putting it in the pot. I then score it once it is in the pot. When I do this, I use my larger cocotte so the edges of the bread don't get a wrinkle from the parchment.

This happened to me! New yeast, thats what I needed.

i have made the same no-knead bread about a dozen times and the only time it was really dense/flat was when i let it sit longer than 24 hours (around 36) before starting final process. this seems to agree with earlier comment, but i too have no idea why that would be the case.

My suspicion is that the dough is over-rising. Gluten is what lets the loaf hold on to those bubbles, and because of the way no-knead develops gluten (by water to flour contact instead of mechanical mixing) they gluten strength is weaker in no-knead. The dough sits out too long, and volia, the gluten can't hold together the dough, and it gets flabby and has little to no oven spring. I have similar problem if I over yeast my cold ferment pizza dough...

I had the same problem, but I found that a 24 hour fermentation took care of that, with a few provisos. I use bread flour (Dakota Maid), I add a couple tablespoons of wheat gluten, and I punch it down after the first twelve hours. I think that redistributes the yeast and really helps the gluten be extra stretchy. I bake every second day and I'm pretty consistently getting a loaf that almost fills my cheap 5 quart JcPenny dutch oven:

http://www.flickr.com/photos/40964542@N08/5471498203/

im not sure what your problem might be, but i figure that this is a good space to share with everyone that catherine newman's riff on the NYT recipe is absolutely amazing. AND her writing is so funny and charming and true, its like a little treat to read along with a great recipe... http://family.go.com/blog/catherinewman/fantastic-fearless-five-minute-bread-889536/

yikes. lots of misinformation in these comments.
Without knowing more about how you are building your dough, there isn't an answer.
Bread baking is all about the minutae, and what you describe could be happening for about ten different reasons.
No-Knead is basically foolproof even for beginner, so with that in mind my vote is that your yeast is too old.

I followed the Minimalist recipe and had the same problem. Then I checked the recipe in "How to Cook Everything", and he specifies:

1) Use Rapid Rise yeast
2) Use a scant half-teaspoon of yeast. The Minimalist recipe said a quarter-teaspoon.

These changes made all the difference to my bread!