this is a healthy and delicious addition to anybody's diet. you can add spices, sugar, fruit, veggies, anything you want. i also use it in recipes, adding it at the end. many indigenous cultures use fresh yogurt, and for good reason.
combine liquid milk and powdered milk in a pot, put on stove at medium setting.
preheat oven or toaster oven to "warm" setting (100-150 degrees F).
once milk threatens to boil over, remove from stove and cool (in ice bath if desired) so that the pan is not too hot to the touch.
combine milk and yogurt in a very clean tupperware container, cover container.
set container in pre-heated oven, leave for about 6 hours.
your yogurt should be nice and thick-- now store it in the fridge for up to two weeks.
NOTE: The ideal incubation temperature is 115 degrees F, plus or minus 10. Instead of a warm oven, you can use a sunny outdoor spot during summertime. In winter, you can set the container by a radiator or wood stove. Recently I have found the crockpot is a reliable heat source. Simply place water in your crockpot, filling the pot about halfway. Then place the covered yogurt container inside the crockpot, making sure the water does not enter the yogurt. You can then use a thermometer to monitor the water temperature, and adjust your crockpot during the incubation period to maintain ideal temperature.