Sourdough cracking on top

I love making bread but until now haven't had much success with sourdough. I think I've "cracked" it now - the flavor and texture is pretty good but it's cracking on top. I'm using the no knead method, mixing the dough the night before, folding in the morning (can be anything from 12-28 hours) and leaving to prove for an hour or so. My Dutch oven is a little too large for the amount of dough so I put another dish inside it and this work well. 

With my first two attempts the dough was really wet and hard to work with. I changed the recipe (the one I used for this   is from Breadtopia) and the dough is firmer but still a little tacky to touch. I think even although I do slice the dough on top (difficult because it's tacky) the crust would still separate - it almost looks like pork crackling. It's really only cosmetic but guess I'm a perfectionist. 

To cook I heat up the Dutch oven with the second dish inside, bake at 220C for 45 minutes, remove the lid and bake a further 10-15 minutes. I've had to increase the first cook time a further 10 minutes for the last two as it still looked a little doughy. I'm looking forward to exploring your site and trying new recipes.