Rinse the lentils.
Place them into a large stock pot and add 8 cups of water.
Remove the skin from the red onion and cut it in half.
Pin one bay leaf to each onion half using a whole clove.
Add the onion halves to the pot and bring the water to a boil over high heat.
Add 1 tsp salt, reduce heat to a simmer and allow to cook with lid partially covering the pot for about 30 minutes, then turn off the heat and place the lid on all the way.
In the meantime, bring a medium pot of salted water to a boil, carefully place the potato rounds into the water and allow to simmer aggressively until fork-tender, about 10 minutes, then drain them in a colander.
Clean the leeks: Slice off the bottoms and tough top leaves, then slice the white and light green parts into 1/4-inch rounds. Place the leeks into a large bowl and cover with water, allowing the grit from the inside of the leeks to fall to the bottom of the bowl. Remove the leeks to a paper towel and dry well.
Heat the olive oil in a large sauté pan over medium heat, then add cleaned leeks. Season with salt and pepper and cook, stirring frequently, for about 5 minutes until soft.
Add garlic, rosemary sprig and smoked paprika and stir to coat the leeks.
Add the saffron or cumin along with the 1/4 cup room temperature water it was soaking in, then the crushed tomatoes and vinegar.
Turn heat up and simmer for a couple of minutes to allow the flavors to combine.
Pour the leek tomato mixture into the pot with the lentil and onion broth and stir to combine.
Add the drained potatoes and stir, then bring everything to a vigorous simmer and allow to cook for about 10 more minute.
Check to make sure the lentils are soft and the potatoes are heated through, then discard the onions, bay leaves, cloves and rosemary sprig.
Ladle portions into bowls and serve.
