Preheat the oven to 400 degrees F.
Piece the sweet potatoes all over with a fork and wrap each one tightly in foil. Place on a baking sheet and roast until the flesh gives easily when pressed, about 1 hour. Unwrap and set aside to cool completely.
To make the za’atar, toast the sesame seeds in a small skillet over low heat until golden and fragrant, about 3 minutes. Transfer to a bowl and add the thyme, sumac, and 1/4 teaspoon salt. Stir and set aside.
Peel the sweet potatoes and place them in a food processor. Add the tahini, water, lemon juice, hot sauce, a few turns of pepper, and 2 teaspoons of the prepared za’atar. Puree until completely smooth. Taste and season with more salt and pepper if needed.
Scrape the dip into a small serving bowl, drizzle with the oil, and sprinkle with a teaspoon of the za’atar. Serve alongside crackers and crudités, or warm pita if that’s your bag!