Golden Delicious apples are particularly good here. If you want to use the bacon fat in the salad, eyeball how much fat you think there is and reduce the olive oil by that amount.
3 lbs small potatoes (Yukon Gold, Red Fingerling), quartered
5 (thick) strips bacon
1 large red or yellow onion, chopped
2 apples, (peeled), cored, and cut in 1/2-inch dice
4 scallions or chives, thinly sliced
1/2 c olive oil
1/4 c red wine vinegar
1/4 c Dijon mustard
1 T chopped fresh thyme or 1 t dried
salt and ground black pepper, to taste
1. Combine the potatoes and enough cold water to cover by a couple of inches in a large saucepan. Add a generous pinch of salt, if you like. Bring to a boil, lower the heat, and cover the pan. Simmer for 15 minutes, or until the potatoes are tender when pierced with a fork. Drain well.
2. While the potatoes are simmering, cook the bacon in a large skillet over medium heat. Once cooked, remove the bacon to a plate lined with paper towels. Reserve the bacon fat in the skillet. Once the bacon is cool, chop it.
3. Cook the onion in the bacon fat on medium heat until softened and just starting to brown. Use a slotted spoon to remove the onion from the pan to a large bowl; or scrape the onions and bacon fat into the bowl. Add the chopped apple to the bowl. Add the potatoes, chopped bacon, and scallions. Toss gently.
4. Combine the olive oil, red wine vinegar, Dijon mustard, thyme, salt, and pepper in a small bowl or jar. Pour over ingredients in large bowl. Toss gently to combine. Serve warm, at room temperature, or cold.