Preheat an oven to 350 F.
Sear the beef. Heat the oil in a dutch oven over medium-high heat. Pat the cubes of beef dry and season liberally with salt and pepper. Once the oil is hot, add the cubes of beef in a single layer and sear the beef on all sides until browned. You may need to do this in batches. Remove the beef from the pan and transfer to a plate.
Make the herb bundle. Use kitchen twine to tie the rosemary and thyme sprigs together and set aside.
Saute veggies. Reduce the heat to medium low and add the butter. Once the butter is melted, add the onions and leeks and stir to coat in the fat. Cook for 3-4 minutes, stirring occasionally, until the veggies are soft. Stir in the garlic and cook for another minute.
Build the braising liquid. Stir in the tomato paste, dijon, and the beef bouillon paste until the veggies are well coated. Sprinkle in the flour and cook for another 2-3 minutes stirring often. Pour in the wine, stir well, and bring to simmer. Scrape up any browned bits from the bottom of the pot. Stir in the beef broth and then add the bay leaves and herb bundle.
Braise. Add the beef back to the pot and any juices that accumulated on the plate. Cover and transfer to the oven for 2 hours.
Make the horseradish sauce. In a small bowl, whisk together all the ingredients until smooth and season to taste with salt and pepper. Refrigerate until ready to serve.
Add the veggies. Remove the beef from the oven and stir in the potatoes, carrots, parsnip, and turnip. Cover and return to the oven for another hour or so, until the beef is very tender. Remove from the oven and let the beef stew rest for 30 minutes covered.
Serve. Season the stew to taste and add any additional salt or pepper as needed. Serve warm topped with the horseradish cream sauce.