For pretzel croutons: Place pretzel pieces and oil into a large mixing bowl and season with salt and pepper. Toss together. Spread onto a baking sheet, in a single layer, and toast for 15 to 20 minutes or until light and crisp. Remove from oven and allow pretzel bits to cool.
For vinaigrette: Place a small sauté pan over medium-high heat and melt butter. Add pancetta and sauté for 3 to 4 minutes or until pancetta browns. Pour contents into a mixing bowl and add remaining vinaigrette ingredients, except oil. Whisk together and add oil in a slow and steady stream until fully incorporated. Adjust seasonings and set aside until ready to use.
To assemble: Place Brussels sprouts, pretzel croutons, cherry tomatoes and goat cheese (if using) into a large salad bowl and toss together with vinaigrette. Adjust seasonings and allow salad to sit for about 10 minutes before tossing one more time and serving.