Preheat oven to 425F and lightly grease a large sheet pan. Set aside.
Cook bacon in a single layer in a medium skillet over medium heat, turning occasionally until bacon is crispy, about 5-8 minutes of cooking. Drain bacon on paper towels then finely chop. Reserve bacon drippings.
To prepare the leeks, cut and discard the stem and the tough green parts. Slice the white and light green parts into 1/2-inch slices, place in a bowl of cold water, and lightly toss to remove any dirt. Allow leeks to soak in water 10 minutes. Drain leeks, rinse well with cold water, and pat dry.
In a large bowl, combine sliced leeks, baby potatoes, bacon drippings, mustard, rosemary, and salt and pepper to taste. Lightly toss until everything is evenly coated.
Arrange potatoes and leeks in a single layer on prepared sheet pan with the cut-side of potatoes down. Roast potatoes and leeks at 425F 25-30 minutes until potatoes and leeks are crispy and golden-brown.
Sprinkle potatoes and leeks with minced garlic and crispy bacon bits and toss to combine. Serve warm and enjoy!