Position oven racks in the center and top third of the oven and preheat to 325 degrees F. Spread the almonds, sunflower seeds and pumpkin seeds on a baking sheet. Bake for about 12 minutes. Stir together the toasted nuts, rolled oats, flax seeds, sesame seeds and raisins (if using) in a large bowl. Brush the 2 baking sheets with oil or shortening to prevent sticking.
Dissolve the corn starch in cold water and set aside. Place the sugar and oil in a small saucepan set over medium heat. Bring to a low boil, stir briefly and be sure it is boiling all the way into the center of the syrup. Mix in corn starch. Immediately pour over the oat and nut mixture and stir till completely, thoroughly coated.
Spread evenly on the cookie sheets. Bake, stirring every 10 minutes or so, until nicely browned, about 30 minutes. Cool on the pan - stir briefly after about 10 minutes to prevent sticking, then cool completely on the pan for small chunks to form.
(The granola can be stored in an airtight container at room temperature for up to 1 month, or in the freezer for up to 3 months.) Serve in bowls, adding your favorite dried fruit, if desired.