How to Enjoy Milk in Your Hot Cereal When You're Lactose-Intolerant.
The deal
So, you like milk in your hot cereal, but it doesn't like you. Fortunately, there's a trick to allow you to continue using milk with the likes of oatmeal, farina, rice (pudding), grits, bulgur wheat, cracked wheat, sorghum, barley, and more without resorting to watery milk substitutes.
Heavy cream explained
If you didn't already know, heavy cream is commonly used to make whipped cream, and is used widely in sweet and savory cooking. Shaking heavy cream for several minutes will eventually yield butter and buttermilk as the fat separates from the liquid, respectively. By combining the unadulterated cream with water, we can approximate the flavor, consistency, mouth feel, and appearance of whole milk without upsetting your stomach.
How to do it
You'll want three parts water to one part heavy cream, though you can increase the proportion of heavy cream, if desired. So, for example, if you're using 1 cup of water, you'll probably want at least 1/3 cup of heavy cream. I tend to add enough cream where it becomes no longer clear that you used any water. After you've used this technique for a while, you'll be able to eyeball and/or tell by taste.
A side effect of this approach is that the cereal can wind up being thicker than it would be with milk, which may or may not be what you want. I will note that this thickness makes the cereal more accepting of fruit juices than it would be if milk were used.
The cooking method is up to you, be it microwave, stovetop, or something else. You would cook the grains in water, then add heavy cream. Adding the cream separately eliminates any possibility of scalding, reduces the chance of overflow, and ensures a more efficient heating. This means you could either cook the grains in the the liquid or add the grains to the cooked liquid. You can optionally reheat the cereal after the cream has been added. If desired, you can still add fruit, sweeteners, or other condiments, including butter, at the end. I find that a pinch of salt accentuates the sweetness, but you can safely leave it out.
Bonus tip
Another trick that some folks use is to soak the grain prior to cooking. Some soak overnight, but I've found that even an hour or less has at least some softening effect. Soaking may also reduce the potential for the cereal to boil over. More importantly, this trick makes the grains easier for the body to process, the result being fewer digestive problems.
Why heavy cream works
So, at this point, you may be wondering why this trick works for those suffering from lactose intolerance? Now, while I don't have any scientific data for you, I do have a theory.
So, adding the water allows the grains to cook all the way through and provides a softening effect on the grains, but it should have the added benefit of replacing the lactose sugar that would otherwise be there if whole milk were used exclusively, meaning your stomach will be consuming less lactose. What doesn't exist can't hurt you, right?
Tradeoffs
The topmost disadvantage of using heavy cream is that it usually costs more than the same quantity of milk, however, the advantages may make up for this. First, you've reduced your reliance on medications which treat the symptoms of lactose intolerance, so you've reduced or cut out that cost. Second, you may spend less time in the restroom. If you're able to accept these tradeoffs, bon appetit.