It's easy to roast your own sunflower seeds. The first step is to plant a large-seeded sunflower variety. First, plant a large-seed sunflower variety. 'Snack Mix', 'Mammoth Gray Stripe', 'Humongous', and 'Skyscraper' all produce heavy crops of large seeds. The stalks are quite strong, but it's a good idea to stake sunflowers grown for seeds (strictly ornamental varieties usually don't need support). The enormous seed heads can weigh several pounds, and in windy conditions it's possible for the top-heavy plants to topple.
Bumblebees and other pollinators love to forage for pollen on the oversize faces of sunflower blooms, fertilizing the flowers as they go. Soon the petals will begin to fade. At this point you may need to cover seed heads with a mesh bag (pantyhose works well) to keep out hungry birds, which can quickly devour your crop. Birds are not always an issue, but at the least you should inspect seed heads daily so you know right away if you need to protect the seeds.
The seeds will quickly develop; when mature, they will be plump with hard shells. Then you can cut the entire head off the stalk and store it in a dry place for a few weeks for drying. When completely dry, the seeds should be fairly easy to remove from the seed head. There will be some chaff and other debris, which is simple (if a little tedious) to separate by hand. Then collect all of the seeds in a pot or bowl, and rinse them with water.
Now you're ready to salt and roast your seeds. The following recipe is provided by the National Sunflower Association (sunflowernsa.com):
Cover unshelled sunflower seeds with salted water, using 1/4 to 1/2 cup of salt per 2 quarts of water. Soak seeds in the salt solution overnight. The next morning, drain off the water and pat the seeds dry to remove excess moisture. (You can also roast the seeds unsalted -- simply skip the soaking process.)
Preheat the oven to 300 degrees Fahrenheit. Spread the sunflower seeds evenly on a cookie sheet or in a shallow pan, and bake for 30 to 40 minutes or until golden brown, stirring occasionally. The seeds often develop a small crack down the center as they roast. Taste after each stirring to see if the seeds are completely roasted. After roasting, remove seeds from the oven and allow them to cool completely. Store the seeds in an airtight container for future snacking.
Variations call for mixing a teaspoon of melted butter with a cup of seeds while they are still warm from the oven; these are for immediate eating. You can also experiment with different seasonings, such as barbecue, Cajun, and taco.