In a large saucepan, heat the olive oil over medium-high heat. Add the finely diced onion, carrot, and potato. Sauté for approximately five minutes, stirring occasionally, until the onions become soft and translucent.

Thoroughly rinse the red lentils to remove any debris or excess starch. Add them to the saucepan and sauté for an additional three minutes, stirring continuously to prevent sticking.

Pour in the six cups of water, then add the stock cubes. Stir well to dissolve. Next, add the dried mint, cumin, paprika, turmeric, cayenne pepper (if using), salt, and black pepper. Stir to combine. Bring the mixture to a boil, then reduce the heat to medium. Allow the soup to simmer uncovered for approximately 25-30 minutes, or until the lentils and vegetables are completely tender. Stir occasionally to ensure even cooking.

In a separate small skillet, melt the butter over medium heat. Once melted, add the flour and whisk continuously until the mixture forms a smooth paste and begins to bubble slightly. This process should take about 1-2 minutes.

Once the soup has finished cooking, use an immersion blender to blend the mixture until it reaches the desired consistency. If a smooth texture is preferred, blend until completely creamy. For a chunkier soup, pulse the blender a few times, leaving some vegetable pieces intact. If using a standard blender, allow the soup to cool slightly before blending in batches to avoid splattering.

Taste the soup and adjust the seasoning if needed, adding additional salt or pepper as desired. Serve warm with a squeeze of fresh lemon and a side of crusty bread or green olives for added flavor.