First, drain the canned diced tomatoes. Remove as much of the liquid as possible, and blend into a fine pulp. Use either an immersion blender or a standard blender to do this.
In a large skillet, pour in the blended tomatoes, extra virgin olive oil, Italian spices, dried basil, garlic, red pepper flakes, and onion salt. Stir well.
Over medium low heat, stirring occasionally, gently simmer the marinara sauce. After about 15 minutes the sauce will reduce and create a thick paste. When you are happy with the texture and thickness, remove from heat and set aside to cool. Remember the longer you cook the sauce, the thicker it will get!
Notes
This pizza sauce can be frozen for up to 3 months in an air tight container or ziplock.