In a small, microwave-safe bowl, sprinkle the gelatin over the water and let stand until softened, about 3 minutes. In a large microwave-safe bowl, whisk the sweet potatoes with the whole milk, heavy cream, condensed milk, brown sugar, and salt. Microwave the sweet potato mixture at high until warm, about 1 minute. Microwave the gelatin mixture at high until melted, about 10 seconds, then whisk it into the sweet potato mixture and let the panna cotta mixture cool.
Lightly rub 6 - 1/2"-inch ramekins with vegetable oil. Pour the panna cotta mixture into the ramekins and refrigerate until firm, at least 2 hours.
In a small bowl, combine the cranberry sauce and cranberry juice. Run the tip of a paring knife around the inside of the ramekins.
To unmold, dip a ramekin into a shallow bowl of hot water for 30 seconds; dry off the ramekin and invert the panna cotta onto a plate. Spoon the cranberry sauce on top and garnish with the cinnamon toast croutons.
Note: The panna cottas can be refrigerated in the ramekins for up to 2 days. Prepare half of the recipe for cinnamon toast crumb crust through step 2 for cinnamon toast croutons.