Preheat the oven to 375 degrees F (190 degrees C).
Place the Sweet Potato (1.5 pound) on a baking sheet lined with aluminum foil and bake for 45 minutes to an hour - or until potatoes are cooked through.
Remove from oven and cut each potato in half. Let the potatoes cool until you can handle them.
Scoop out the flesh into a bowl.
Use a potato ricer or hand mixer to puree the potatoes.
Stir in Fresh Rosemary (1 teaspoon), Kosher Salt (1/2 teaspoon) and Freshly Ground Black Pepper (1/4 teaspoon). Add the Milk (1/4 cup) and Butter (1 tablespoon) and stir until butter is melted.
Add Gruyère Cheese (1 1/4 cup) stir to combine. Set aside.
Spray 4 half-cup ramekins with vegetable spray. Divide the sweet potatoes among the ramekins and smooth the tops with the back of a spoon. Sprinkle with the remaining Gruyère Cheese (1/4 cup).
To bake the gratins, preheat the oven to 350 degrees F (180 degrees C).
Place the gratins on a baking sheet and bake for 15 minutes until warmed through.
Then turn on the broiler and cook for an additional 2-3 minutes until lightly browned. Serve and enjoy!