Preheat oven to 350 degrees. Spray baking dish with non-stick cooking spray and set aside.
To make the praline sauce: melt butter in small saucepan over medium-low heat. Add brown sugar, heavy cream, cinnamon, nutmeg, and sea salt, and stir until mixture is uniform. Bring sauce to a boil then reduce heat to low and simmer for 5 to 10 minutes to allow sauce to thicken. Remove from heat.
Meanwhile, peel and slice sweet potatoes.
Arrange sweet potato slices in baking dish in an overlapping scalloped pattern then pour praline sauce over top.
Cover dish with foil then place in oven to bake for 30 minutes. Remove foil and return dish to oven uncovered to bake for another 30 minutes or until sweet potatoes are fork tender and sauce is golden and bubbly.
Garnish with pecan pieces and serve warm.
Notes
PreparationSlide a sheet pan onto the rack below the baking dish to catch any drips.To make arranging the sliced sweet potatoes easier, place them in a horizontal stack, standing up on their sides, then flick the stack over to fan them out into an overlapping line. Repeat until you've used all the slices.Making AheadYou can make the praline sauce ahead of time and store in the fridge until you're ready to assemble the gratin bake. Just warm it back up and stir well to reconcile any separation.Keep in mind that some separation may occur with the praline sauce so for the absolute best presentation and taste, I don't recommend making this entire dish in advance. But you can make this dish up to two days ahead of time, refrigerate, and warm it back up in the oven.StorageStore any leftovers in an airtight container refrigerated. They last in the fridge for up to five days.You can freeze praline candied yams for up to three months using an airtight, freezer-safe container. Note that the texture is usually much softer after thawing.