Image credit to: Karlihearts (via Instagram)
Preheat oven to 450 degrees F with rack in upper third of oven. Line a baking sheet with parchment paper and preheat with the oven.
Put sweet potatoes and garlic in a large bowl. Toss with 3 Tbsp oil, sprinkle generously with coarse salt, then toss again. Spread potatoes evenly on the lined baking sheet and place in the oven. Bake for 10 minutes, turn potatoes over, and bake for another 5-10 minutes or until potatoes are tender and browning and spots.
Meanwhile, heat remaining oil in a small heavy skillet over medium-high heat until it shimmers, then fry sage leaves in 2 batches, stirring, until crisp, 30 seconds to 1 minute per batch. Transfer with a slotted spoon or tongs to paper towels to drain. Remove pan from heat, reserving oil.
Roughly crumble fried sage over the potatoes, add more coarse salt to taste, and serve immediately.