Home-Made Cream Cheese
Pour a container of home-made or store bought whole milk plain yogurt into a muslin-lined seive or jelly strainer with a bowl underneathe. Let the whey drain out for several hours. What's left in the muslin is cream cheese! You can use the whey to soak your grains (Read Nourishing Traditions by Sally Fallon for how and why you should do this.)
Home-made Sour Cream
Pour some of the finest cream you can buy (not ultra-pasteurized) into a glass mason jar. Add some of the finest cultured buttermilk you can find (not fat-free). Cover and let it sit on your countertop for 24 hours before transferring to the fridge. It may be liquidy at first, but should solid up into sour cream. I'm not sure what ratio to use. I just kind of eyeball it, but I'd say for every cup of cream, use at least 2 tablespoons of buttermilk.