Step one: Make yourself some homemade bread
Step two: Slice a nice thick slice. Cut it into chunks.
Step three: Heat oven to 350 F.
Put down some parchment paper on a cookie sheet. Spray with olive oil. Sprinkle sea salt on oil. Pick up bread chunks. Shake off the bitty pieces that will only burn and cause your fire alarms to go off really loud when you open the oven to check on the croutons. Spread out chunks on cookie sheets. Spray and salt tops of bread chunks.
Put in oven for 5-6 minutes. Pull out, flip chunks over, put back in over for 4-6 more minutes. Depending on the bread you use, the cookie sheet, and the size of the chunks, you will have to adjust the times to fit your needs.
These can be stored for up to a week (the longest they've ever lasted in my house) but will need to be tossed into the oven or toaster oven to re-crisp. Sometimes, I just make enough for a salad in the toaster oven and I set it at 400F.
You'll never be able to eat croutons from the store again.