Peel the celeriac and cut it into small cubes. Place in a large pot of lightly salted water and bring to a boil. Cook until the celeriac is almost tender. Add the sauerkraut during the last few minutes of cooking to heat it through.
Meanwhile, heat the smoked sausage according to the package instructions.
Cook the diced bacon in a skillet over medium heat until golden and crispy. Transfer to a plate lined with paper towels to drain, reserving the rendered bacon fat.
Drain the celeriac and sauerkraut well. Using a potato masher, mash them together until combined but still slightly chunky.
Stir in the crispy bacon, a little of the reserved bacon fat, and the pineapple cubes. Season with salt and black pepper to taste.
Serve the sauerkraut mash warm with the smoked sausage on the side.
Notes
Using potatoes instead of celeriac: For a more traditional Dutch stamppot, replace the celeriac with regular potatoes. Yukon Gold potatoes are a great choice because they mash beautifully.For a creamier mash: Instead of using the reserved bacon fat, add a little butter and milk until the mash reaches your preferred consistency.About the smoked sausage: Dutch rookworst is a traditional smoked sausage commonly served with stamppot. If you can't find it in the United States, kielbasa or another fully cooked smoked sausage makes a good substitute.