I made Nigella's Chocolate Fudge Cake in Australia and it was moist and beautiful. However now I live in San Diego and when I made the cake it was completely different, it was dry and broke up. Any ideas?
Nigella's Chocolate Fudge Cake (from Nigella Bites) is hugely popular as it normally comes out as a rich moist cake base with a rich fudge frosting. Unfortunately whenever anyone moves house, whether within the same country or to a different country, there will always be a variance in equipment and ingredients and sometimes you will need to bake a few cakes to get a feel for the new environment.
Make sure that you are using the regular (full fat) sour cream and not a low fat version and you should be using all-purpose flour in the US. However we suspect that the issue lies less with the ingredients and it is more likely that the oven you are using may be a little too hot which means that the cake could have been over-baked and become dry. If possible check the oven temperature with an oven thermometer (they are relatively inexpensive) and if you have a convestion or fan-assisted oven then check the manufacturer's handbook to see if they have any advice on adjusting the oven temperature for cakes. Also check the cake 5 minutes before the end of th stated cooking time as the cake may be baking more quickly than in your old oven.
If you are baking the cake at high altitude (above 1,000m/3,000 feet) then this could also affect the cake as at high altitude liquid evaporates more quickly and give a dryer cake. As a general guideline you need to add 1-2 tablespoons extra liquid (such as water or egg white) to the cake batter per cup of liquid. So in this cake you would need to increase the egg content by 1 tablespoon and the water by 1 tablespoon. And again you should start checking the cake early as it will bake more quickly at higher altitude.