Melt the butter in a medium sauté pan. then cook the sliced red onions for about 5 minutes if you like your onions firm or 15 minutes if you like your onions like onion jam.
Season with some rub then add the Cabernet and simmer until reduced to a syrupy liquid. Remove from the heat and set aside.
Divide the beef into three portions of about ⅓ pound (135g) for each patty.
Shape each beef portion with your hands into a round patty about 1/2-inch (1.3cm) wider in diameter than your bun. Tip: Make a depression in the middle of the patty. This will help ensure that the middle will not bulge out after cooking.
Sprinkle the patty with some rub on both sides and place on a wax paper-lined cookie sheet. Cover in plastic wrap and leave in the fridge until ready to cook.
Heat your grill to 450 degrees F (230 degrees C). Ensure that your grates are cleaned and oiled before cooking to reduce sticking.
Place the patties onto the hot grill, close the grill cover, and wait until they develop a nice char, about 5 minutes. Some flaming is normal as the grease drips, but if it flames excessively move the patty to another spot where it is not flaming.
After about 5 minutes, flip over and repeat to get a nice char on the other side. After the char has developed on the second side, move the patty to a cooler spot on your grill and cook until the internal temperature is about 150 degrees F (65 degrees C) or until there is no pink in the middle.
During the last minute of cooking, add some of the crumbled Gorgonzola cheese and wait until the cheese melts. Remove.
Toast the inside surfaces of your burger buns on your grill. Remove once toasted and browned.
In a small bowl, combine the mayonnaise and sriracha hot sauce.
Spread some of the spicy mayo on your buns, add greens of your choice on the bottom half, add your melted Gorgonzola beef patty, top with Cabernet onions, more spicy mayo, and the top half of your bun.