Peel and cut potatoes into 1-inch chunks, peel and slice carrots into rounds about 1/4-inch thick, dice the onion into medium pieces, slice mushrooms into 1/4-inch pieces, and mince garlic cloves. Measure out the lentils, tomato paste, flour, dried herbs, salt, pepper, and stout. Having everything prepped and ready will make the cooking process smooth and allow you to focus on building flavor.

Heat the olive oil in a large pot or Dutch oven over medium heat. Add the diced onion and carrot slices, stirring occasionally, and cook for about 6 minutes until they begin to soften and the onion becomes translucent. This initial sauté develops sweetness in the vegetables and creates a flavor foundation for the entire stew.

Stir in the sliced mushrooms, minced garlic, and tomato paste, cooking for about 4 minutes until the mushrooms release their moisture and the mixture becomes fragrant. The tomato paste will start to caramelize slightly against the pot bottom, adding deep umami richness—I find this moment is crucial for developing the stew's complex flavor profile.

Sprinkle the flour over the vegetable mixture and stir constantly for about 1 minute to coat everything evenly. This flour will act as a thickener for the stew. Add the dried thyme, rosemary, salt, and pepper, stirring well to distribute the herbs throughout. The flour coating allows the starch to cook out and thicken the liquid later without creating lumps.

Pour in the stout and use a wooden spoon to scrape up any browned bits stuck to the bottom of the pot—this deglazing step releases concentrated flavors that would otherwise be wasted. The alcohol will cook off during simmering, leaving behind the malty depth that makes a proper Irish stew so distinctive.

Add the prepared potatoes and lentils, then pour in the vegetable broth. Bring the mixture to a boil over medium-high heat, then reduce to medium-low and simmer uncovered for 45 minutes, stirring occasionally. The potatoes and lentils will become tender and begin to break down slightly, thickening the stew naturally while the flavors meld together. I like to start checking the potatoes around the 40-minute mark—they should be fork-tender but not falling apart.

Once the potatoes and lentils are tender, taste the stew and adjust seasoning if needed. If the stew seems too thick, add more broth a splash at a time; if it's too thin, simmer uncovered for another 10-15 minutes to reduce. Stir in the fresh parsley just before serving for brightness and color. Serve in bowls with crusty bread alongside for soaking up the rich, flavorful broth.