Place the unpeeled potatoes in a large pot and cover them with salted water by about 1 inch. Bring to a boil over medium-high heat. Cook until tender but firm, about 15 to 25 minutes. Drain and cut into 1 1/2-inch pieces while warm. Transfer to a large mixing bowl.

While the potatoes are cooking, heat a large skillet over medium-high heat and cook the diced bacon until crispy. Remove the bacon with a slotted spoon and place it on a paper towel-lined plate to drain.

In the same skillet with the bacon fat, add the sliced shallots and cook for about a minute until slightly crisp. Remove from heat.

In a bowl, combine mustard, red wine vinegar, salt, and black pepper. Stir in the shallots and bacon fat. Crumble the bacon into the mixture and stir well.

Toss the warm potatoes with the dressing, ensuring they are evenly coated. Adjust seasoning if needed. Garnish with chopped parsley and additional vinegar, if desired. Serve warm or at room temperature.