Preheat oven to 375 degrees Fahrenheit.
Prepare a baking dish by spraying with cooking spray to prevent the potatoes from sticking, and set aside.
Wash, peel, and then thinly slice purple sweet potatoes using a mandoline or food processor.
Soak potato slices in a large bowl of cold water while preparing the rest of the ingredients. This prevents the potatoes from oxidizing.
Pour the evaporated milk into a small sauce pan and add the 2 teaspoons of Old St Augustine Datil Jerk Jamaican Seasoning Blend. Stir to incorporate the seasoning into the milk. Heat the evaporated milk over medium-low heat, stirring frequently, until just gently simmering. Do not boil or the milk will curdle. Remove from heat.
In a skillet, saute the onions in the tablespoon of butter until translucent but not browned.
Add the garlic to the skillet and cook another 3-4 minutes to release the flavor of the garlic. Remove from the heat.
Drain the potato slices.
Stir the milk and pour a small amount into the prepared baking dish.
Top with one third of the potatoes.
Layer half of the onions on top of the potatoes and sprinkle with one third of the cheese.
Add another layer of potatoes and the rest of the onions and sprinkle with cheese.
Top with the remaining potato slices.
Pour the warm milk over the potatoes
Top with the remaining cheese.
Cover casserole dish loosely with foil.
Bake at 375 degrees for 45 minutes. Remove foil and continue to bake for another 15 minutes, or until the cheese is golden and bubbly. You can insert a toothpick into the potatoes to test for doneness. The potatoes should be soft, but not mushy.
