First, slice the top root of your onions off. Then slice the onion in half pole to pole. If you are unfamiliar with this, if the onion was the Earth, slice it as if you were slicing from the North Pole to South Pole. Don't slice them along the equator. This will help the onions from becoming mushy.Peel the onions, cut off the bottom root and then julienne / slice them (again pole to pole) so they are about 1/8 - 1/4 inch thick.
Melt the vegan butter in a large dutch oven or wide skillet. You can also use two separate pots or pans if you have the stovetop space. This will speed things up.
Add the onions, stir to coat them in the butter. Add a few pinches of salt, stir again. And now, we wait. At first, you can crank the heat to medium high, this will speed up the process. Just stir the onions every minute or so.
After about 15 - 20 minutes, you should see some browning, and some fond sticking to the pan. This is a good time to lower the heat to medium or medium low if need be.Then simply cook them until they are golden brown, keeping an eye on the heat and adjusting as needed. The total time for cooking these can take anywhere from 40 minutes to 1 hour and 20 minutes.
Deglaze with some optional Brandy or Cognac (don't worry about this if you don't have any or don't drink it's optional!) Followed by the Vegan Beef or Veggie Broth, Worcestershire, and Thyme. Cook down the liquid until it's mostly reduced down. Remove the onions from the pan and set aside.
Mac & Cheese
Cook the pasta according to package instructions. The cheese sauce comes together relatively quickly, so you should be able to cook it while the pasta water comes to a boil and the pasta cooks. You can also prepare the cheese sauce, then keep it on low while the pasta cooks. Do whatever you prefer!
To the pan that you cooked the onions in, add the vegan butter and melt. Stir in the Red Wine Vinegar.Then add in about 1/4 cup of the flour and whisk together to combine. Add in another 1/4 cup or so of flour and whisk to combine, and repeat this until all the flour has been whisked in. The texture should be like wet sand, cook that for 1 minute to get rid of the raw flour taste.
Add in about 1/2 cup of the plant milk, and just like the flour, we are going to add some and whisk it, then add in more and whisk again, until it has all been incorporated. The mixture will be very thick at first, but don't worry, once all the liquid has been stirred in, it should be nice and smooth. You can always add a splash more milk if it feels too thick.
Add in the Dijon Mustard and Vegan Cheese and whisk until fully melted. Then stir in the caramelized onions, and the cooked pasta. If it feels too thick, you can loosen it up with some more milk or pasta water, just get it how you like it and enjoy!
Broiled Mac & Cheese
To broil this, simply sprinkle on some more vegan cheese shreds on top, add it to the oven under the broiler. Keep an eye on it so it doesn't burn, but once the cheese is melted and browned you are good to go! Just let it cool for 5 - 10 minutes so you don't burn your mouth!
Notes
Cheese - For the cheese, use your favorite Vegan Cheese! I like Follow Your Heart, I've used their Mozzarella, Gouda and Parmesan in this and it works out great. Go easy on the Gouda as too much will overpower the sauce.