Pick through the beans making sure there are no rocks or broken or shriveled beans in the mix. Soak overnight in plenty of water. Strain and rinse.

Saute the onion in the butter with salt until just lightly starting to brown, about 20 minutes. Add in the zucchini and cook another 10 or so minutes until everything looks a shade or two darker. Add the mushrooms and cook another 7-10 minutes. It should look like the pictures above.

Add in the garlic and cook 3 minutes. Add the tomato paste and stir well until everything is coated. Cook 3-5 minutes stirring often. Add in the crushed tomatoes and mix to combine everything. Stir in the oregano, vinegar, mustard, and brown sugar. Mix in the beans, and add a solid 3-5 cups of water until the beans are well covered by a thin liquid. Cover the pot and toss it in the oven. Bake at 300 for 6 hours, checking every few hours and adding water if needed. (you can do this on the stovetop if needed, or in a slow cooker, but I like doing this stage in the oven because I think it makes for a better flavor and is easier.)

Check the beans for tenderness (just so you know what you are dealing with tomorrow) and cool them down quickly. I poured them into a cold slow cooker pot and used a zip-lock bag full of ice to stir them with just to make sure they cooled quickly and safely. Refrigerate overnight.

The next day, get them into the slow cooker on high and stir in half of the parm. Depending on how tender or not tender they are, do this only an hour or two before the party, or as early as 4-5 hours before. Mine needed a full 4 hours to be the texture I desired.

When the beans are ready, stir in the rest of the parm and taste for seasoning. Add more parm, mustard, sugar, or salt, as needed. Serve hot with tasty grilled foods.