Yes, you can. All sunflowers (Helianthus) have edible seeds, but for easier eating, grow a variety that has big seeds instead of the ornamental types, which have small seeds. After the flowers have bloomed and the petals around the edge of the flower have wilted, watch for the back of the flower head to turn yellow. At that point, cut the head, leaving some stalk attached, and hang it in a warm, dry area until it is brown and dry. If you leave it on the stalk to dry outside, it may rot, or birds may eat the seeds before it's time to harvest them. When the head is dry, rub the seeds out over a bag. If you do it carefully, you can use the dry, seedless head as an interesting decoration. Then shell the seeds and roast them or eat them raw.