Heat about 1 Tbsp. of oil in a pan/skillet. Add in the sliced onions, slowly adding in the wine and broth over the course of about 45 minutes to an hour. Constantly stirring.
Add in garlic and all of your seasonings, allow to cook for another minute or two until the garlic becomes fragrant.
Remove from the heat and add in sour cream and mayonnaise missing together until completely combined.
For the bread heat your oven to 375˚, spread shredded cheese over the sliced baguette and bake until the bread is toasted and cheese is melted, about 5 minutes.