Preheat an oven to 375. Spread out the potatoes and garlic on a cookie sheet. Sprinkle with olive oil, toss with your hands to combine. Roast for about 45 minutes, stirring occasionally, until the potatoes are tender. Remove from oven and cool for 15 minutes.

Reserve 1/2 cup of the Gruyère, then toss the remaining cheeses together.

Peel the garlic cloves, then add to a food processor along with the sweet potatoes. Puree until smooth.

Using either a stand mixture or a handheld mixture, whip the egg whites until medium peaks form.

In a saucepan over medium heat, melt the butter. Whisk in the flour and cook until it is pale golden. Slowly add in milk, then whisk until smooth and the mixture is very thick.

Add in the cheeses, one handful at a time, waiting to add the next handful until the previous one is fully melted and incorporated. Add the sweet potato mixture, stir, then add the egg yolks.

Fold in the whipped egg whites, 1/3 at a time.

Spray a 3 quart dish with cooking spray. Carefully pour the soufflé mixture in, then bake for 35 minutes, or until the top is set and golden brown. Sprinkle the reserved Gruyere cheese over the top; bake for an additional 10 minutes.

Remove from oven, sprinkle with herbs, and serve immediately.