Watch the Fat Content in Your Base
The ratio of fat content to gelatin is key to a perfect panna cotta, but don't let that scare you away from playing around with the creamy ingredients you choose for your dish. While cream is preferred, panna cotta can also be made with milk, half-and-half, buttermilk and even low-fat options. Panna cotta is also friendly to dairy alternative substitutions, such as coconut milk (or cream), soy milk, or your favorite nut milk (such as almond or hazelnut).
The lower the fat content, especially if you use low-fat milk or milk alternative, the more likely you'll need to increase the amount of gelatin used to keep your ratios in balance -- depending on the fat content of your milk or cream of choice you may need as little as half a teaspoon to as much 3 teaspoons of gelatin per cup of milk to achieve the desired "jiggle"' [source: Parsons].