Heat your oven to 200 c (400 f) and line a baking sheet with parchment paper. 

Thoroughly scrub and rinse the sweet potatoes to remove any dirt from the skin.  

Half the sweet potatoes lengthwise (and trim the ends if they are not so fresh) 

Drizzle the pan with most of the olive oil, scatter the pan with kosher salt and thyme sprigs. 

Lay the sweet potato halves, cut side down, making sure the cut side is coated in oil (you’re basically frying in the oven) Also, make sure all the thyme sprigs are covered in sweet potatoes or they will burn. There should be even space between the sweet potatoes. 

Brush or drizzle the remaining olive oil on the skin side or the sweet potatoes.

Bake 40-50 minutes until the flesh is completely tender and soft and the sides are slightly burnt and crisp. Exact baking times might vary so if you don’t get the crispy edges just continue baking for a couple more minutes. 

Remove from the oven, allow to cool for 5 minutes then turn over and serve (the skin is now completely edible!)