2 tablespoons canola oil
4 small onions, chopped
1 small shallot, finely chopped
3 tablespoons balsamic vinegar
1/2 teaspoon kosher salt
1/4 teaspoon freshly ground pepper
½ teaspoon dried thyme
1 (8-ounce) package cream cheese, softened to room temperature
1/2 cup sour cream
2 tablespoons mayonnaise
Assorted raw vegetables for serving—baby carrots, sliced cucumbers, small red radishes, fresh mushrooms and grape tomatoes
Over medium heat, heat oil in a heavy-bottom pan or Dutch oven. Add onions and shallot. Let cook until onions are very soft and caramel in color, 45 to 60 minutes.
Add vinegar and thyme; let cook until slightly reduced and thickened, about 15 minutes. Season with salt and pepper; remove from heat and let cool to room temperature.
Meanwhile, in the bowl of an electric mixer fitted with the whisk attachment, whisk together cream cheese, sour cream, and mayonnaise until fluffy, about 5 minutes. Add cooled onions and stir to combine. Transfer to refrigerator to chill at least 2 hours and up to 2 weeks; serve with raw vegetables, flatbreads, or crackers.