Wash the tomatoes, mushrooms, and peppers well under clean running water.

Cut the tomatoes in half, remove the cores, and place them into a large saucepan over medium heat. Crush the first few tomatoes with the back of your spoon as they heat to release the juice, and occasionally stir to prevent sticking.

Once all the tomatoes are in the pot, bring it to a boil over medium-high heat, and cook for 20 minutes. Then, turn off the heat, and let the tomatoes cool slightly before straining out the seeds and skins.

Prepare the rest of the vegetables while the tomatoes are cooking:

Cut the mushrooms into 1/4-inch slices.

Peel the onion, chop it into 1/4-inch pieces, and measure 1 cup of chopped onions.

Remove the stems and seeds, chop the pepper into 1/4-inch pieces, and measure 1 cup of chopped peppers.

Remove the papery skins, trim the root end, and mince the garlic.

Once the cooked tomatoes have cooled slightly, remove the skins and seeds with a food strainer, food mill, or sieve. Return the strained tomatoes to the saucepan.

Heat olive oil in a large skillet over medium-high heat. Add the mushrooms, onions, peppers, garlic, and sauté until tender.

Add the sautéed vegetables to the pot of tomatoes along with the brown sugar, parsley, oregano, salt, and pepper.

Bring the pot to a boil over medium-high heat, and then reduce the heat to low. Simmer uncovered until the sauce thickens and reduces by one-half. This will take 1 to 2 hours, depending on how juicy your tomatoes are. As the sauce simmers, frequently stir to prevent sticking.

Wash the jars, lids, and rings in hot soapy water and rinse thoroughly. Set the lids and rings aside until you are ready to use them.

Place the jar rack into the pressure canner, and fill with water per your pressure canner manufacturer's instructions: Presto is 3 quarts, Mirro is 2 quarts, and All American is 2 to 3 inches.

Fill the jars halfway with hot water, and then place them on the rack in the canner. Bring the canner to a simmer for 10 minutes (180˚F). Keep hot until you are ready to fill them.

Spread a kitchen towel on the counter. Use your jar lifter to remove a jar from the canner. Pour out the water (save it for washing dishes), and place the jar on the towel. Keep the remaining jars in the canner so they stay hot.

Use the ladle and canning funnel and fill the jar with the hot spaghetti sauce leaving 1-inch headspace.

Run the bubble popper through the jar to release air bubbles, adjust headspace if needed, wipe the rim, center a lid on the jar, and screw on the band until it is fingertip tight.

Place the jar back into the canner, and repeat with the remaining jars.

Cover the pressure canner and secure the lid. Leave the vent open, adjust the heat to medium-high, and bring the canner to a boil. Allow the pressure canner to vent steam for 10 minutes, then place weight on the vent.

Once the canner has reached the correct pressure (10 pounds for weighted gauge and 11 pounds for dial-gauge pressure canner), set a timer, process pints for 20 minutes, and quarts for 25 minutes at altitudes of less than 1,000 ft. Adjust pressure for your altitude if necessary (see note below). Regulate the heat as needed to maintain steady pressure.

When the processing time is complete, turn off the heat and let the pressure canner cool and depressurize. The time will depend on your brand and should be between 30 to 60 minutes. Follow the instructions for your pressure canner.

Once the pressure canner depressurizes, spread a kitchen towel on the counter, remove the weight from the vent pipe or open the petcock, and wait 10 minutes for the jars to adjust to the change in pressure.

While wearing pot holders, unlock the cover and remove the lid while tilting it away from you so that steam does not burn your face. Allow another 10 minutes for the jars to adjust to the change in pressure.

Use a jar lifter to remove the jars from the canner and place them on the towel. Keep the jars upright, and don't tighten bands or check the seals yet. Let the hot jars sit undisturbed for 12 to 24-hours to cool.

Wait until the jars have cooled for at least 12-hours, and then check to be sure jar lids have sealed. Test the seal by pushing on the center of the cover. The lid should not pop up. If the top flexes up and down, it failed to seal. Refrigerate the jar and use it up within a few days.

Remove the screw-on bands and wash the jars. Label, date, and store the jars of spaghetti sauce in a cool, dark place between 50 to 70˚F. Use within a year for the best quality. This recipe makes about 8-pint jars or 4-quart jars.