How to Make It
Preheat oven to 425°F. Run potatoes through a spiralizer using the fine blade just one size larger than angel hair size to make thin strands; cut strands into pieces no longer than about 6 inches.
Combine potatoes and 3 tablespoons olive oil in a large bowl; toss well to coat. Arrange potato mixture in a single layer on 2 rimmed baking sheets lined with parchment paper. Bake at 425°F until lightly browned, about 18 minutes.
Stir together garlic slices and remaining 1 1/2 teaspoons oil. Divide garlic mixture evenly between the 2 pans; toss gently to combine and to ensure all potato pieces brown evenly. Rotate pans from top rack to bottom rack, and bake until browned and crispy, 10 to 12 minutes, gently stirring every 3 minutes.
Remove pans from oven; combine all potatoes and garlic on 1 pan. Sprinkle with rosemary and salt; toss gently to combine. Serve immediately.