"If you want to kick up your regular burger a few notches and get more dinner-table approval grunts, this is a sure thing. Juicy, super-flavourful, and can be an appetizer (sliders) or full sized burgers. Pour a glass of wine and indulge!
Preheat an outdoor grill for medium-high heat and lightly oil the grate.
Stir mushrooms, shallots, garlic, thyme, salt, and pepper together in a bowl. Heat olive oil in a skillet over medium heat;cook and stir mushroom mixture until golden, about 8 minutes. Pour red wine into skillet; simmer until liquid evaporates, stirring slowly, about 2 minutes. Spread mushroom mixture onto a plate to cool to room temperature, about 5 minutes.
Crumble ground chuck into a bowl; pour truffle oil over beef and massage oil gently into beef until evenly distributed. Fold mushroom mixture into beef mixture until combined; form 6 patties approximately the size of baguette slices.
Grill patties until no longer pink in the center, about 3 minutes per side. An instant-read thermometer inserted into the center should read at least 160 degrees F (70 degrees C).
Toast baguette slices until crisp and golden. Place each patty on a baguette slice, top with 2 shaved slices of Parmesan cheese, about 1/4 cup arugula, and a second baguette slice. Secure each slider with a toothpick.
A couple suggestions I've learned the hard way... don't use extra lean ground beef when grilling because it tends to dry out; especially as leftovers. Fresh herbs are always better when possible. Have everything prepared before you start because the meat cooks so quickly you wouldn't want it to cool off if everything else isn't ready. You can add all sorts of toppings: fancy Dijon mustards or mayo spreads, various cheeses, pickled yummy things, sprouts, cilantro or other baby greens. I like the subtle taste of arugula and find it doesn't compete with the unique taste of the truffle oil.
Try to find a fat baguette, so that your slices will be more round than oval.
If you trust your meat source and have a fabulous chuck instead of ground grocery store beef, then grill your sliders to a perfect medium-rare/medium. Well-done if not.
Parchment can be used for easier cleanup/removal from the pan.