Once olive oil becomes more fluid, add onions and stir them around to coat them well.
Stir them occasionally and cook until onions become translucent. If you want to cook them a bit longer, you can wait until they become a deeper brownish color. This will give the sauce a slightly different, more caramelized flavor.
Turn the heat up to high. Then add in wine. Use your spoon to scrape the bottom of the pan to pull off any bits that have stuck.
After less than a minute, turn the heat back down to medium. Then add in your crushed tomatoes. Then add salt, sugar, black pepper, and crushed red pepper (if you want heat).
Bring the mixture to a simmer and then turn the heat down to medium-low. Adjust sea salt and black pepper to your liking. Remove from heat.
Stir the sauce every few minutes and cover the pan with a lid (but allow for a small area to be open so as to vent out heat). Cook for 8 to 10 minutes. Do not turn the heat up or allow the sauce to boil. It will burn.
Once done, remove from heat and store or use on your favorite dish!