Place sliced onions, peeled/halved garlic cloves, and chile in a quart jar.
Make the brine; in a small pan add sea salt, sugar, peppercorns, and vinegar.
Bring the pickling liquid up to a rapid boil, pour boiling liquid over onions & garlic, chile, in a jar.
Make sure the onions are under the liquid and cool to room temperature.
Once the onions cool, close the lid and store in the refrigerator for up to 3-4 weeks.
Serve it warm.
for the Parmesan vinaigrette:
add all ingredients to a mason jar with a fitted lid and shake. Toss 1 tablespoon of vinaigrette with the cup of lettuce. Set aside.
for grill cheese assembly:
heat a hot griddle, or heavy cast iron pan. Butter French bread with soft butter, sprinkle parmesan cheese on the pan and lay the buttered bread side down on top of the cheese in the pan. Slightly move the bread to get all the cheese on the bread. Grill the bread until it is golden brown and crispy.
Next, spread a layer of whole grain Dijon mustard on one bread side, then top with sliced Brie and allow to melt.
Remove bread slices from pan, and on a plate add heirloom tomato, cornichons, pickled red onions, and pile the salad tossed in vinaigrette, and close the grilled cheese. Enjoy.