Rinse the Brown Lentils under cold water and set aside.
Dice the Smoked Bacon and render it in a large pot over medium heat until golden and crisp; remove most of the bacon leaving about 1–2 tablespoons of fat in the pot.
Add the finely chopped Onion, Carrot, Celeriac and sliced Leek to the bacon fat and sauté until softened and beginning to brown, about 6–8 minutes.
Return the bacon to the pot, add the rinsed lentils, a Bay Leaf, enough Beef Broth and Water to cover the lentils by about 2 cm, bring to a simmer and cook gently until the lentils are tender, about 25–35 minutes; skim foam as needed.
When the lentils are soft, season with a splash of Vinegar, a pinch of Sugar, and salt and freshly ground Black Pepper to taste; simmer a few more minutes so the flavors meld, then remove the bay leaf.
While the lentils cook, make the Spätzle batter: whisk together the Flour, Eggs, a pinch of Salt, a little Water and freshly grated Nutmeg until smooth—batter should be thick but drop easily; let rest 10 minutes.
Bring a large pot of salted water to a rolling boil; press the batter through a Spätzle maker or a coarse-holed colander into the boiling water, cook until the dumplings float plus 1–2 minutes, then scoop out with a slotted spoon into a bowl.
Toss the drained Spätzle with butter: melt Butter in a pan, add the cooked Spätzle and gently sauté until lightly golden and coated.
Heat the Wiener Würstchen by poaching them briefly in the simmering lentils for a few minutes or by warming them separately, then serve the sausages alongside or nestled into bowls of lentils with a generous helping of Spätzle on the side.
