Preheat oven to 425 F. Line baking sheet with foil or parchment paper. Peel and slice sweet potatoes into 1/2-inch rounds. In medium bowl, toss sweet potatoes with oil and lightly season with salt, to taste. Arrange rounds in single layer on prepared pan; bake until sweet potatoes are lightly browned and tender, about 20 minutes, flipping halfway through.

In small skillet over medium heat, bring butter to simmer. Add half the sage leaves. Cook until crispy, 2-3 minutes. Remove to paper towel and season lightly with salt, to taste. Repeat with remaining sage leaves. Reserve 2 teaspoons butter. In small food processor, combine goat cheese and reserved butter; whirl until smooth.

To make rounds, remove goat cheese to plastic zip-top bag. Cut off one corner and pipe small dollops of cheese onto each round. Top with half slice prosciutto and one crispy sage leaf.