Add sesame seeds to a wide, dry saucepan over medium-low heat and toast, stirring constantly until the seeds become fragrant and very lightly colored (not brown), 3 to 5 minutes. Transfer toasted seeds to a baking sheet or large plate and cool completely. (Careful here, sesame seeds can burn quickly). Add sesame seeds to the bowl of a food processor then process until a crumbly paste forms, about 1 minute. Add 3 tablespoons of the oil then process for 2 to 3 minutes more, stopping to scrape the bottom and sides of the food processor a couple times. Check the tahini’s consistency. It should be smooth, not gritty and should be pourable. You may need to process for another minute or add the additional tablespoon of oil. Taste the tahini for seasoning then add salt to taste. Process 5 to 10 seconds to mix it in. Store tahini covered in the refrigerator for one month. You may notice it separates over time, like a natural peanut butter would. If this happens, give the tahini a good stir before using.