Begin by gathering all your ingredients in one place for easy access during cooking. Rinse the lentils under cold water until the water runs clear; this helps remove any debris or impurities from them. While rinsing them, chop all your vegetables—onion, carrots, celery—and mince the garlic cloves so they're ready to go once you start cooking.

Step Two : Sauté Vegetables: In a large pot over medium heat, drizzle about two tablespoons of olive oil. Once hot, add diced onions first; sauté them until they become translucent—about 5 minutes is sufficient. Next add sliced carrots and chopped celery; continue cooking while stirring occasionally for another 5 minutes until softened slightly.

Incorporate minced garlic into this mixture now; let it cook for around one minute until fragrant—be cautious not to burn it! The foundation is set with these aromatic ingredients; they will infuse lovely flavors into your stew.

Step Three : Add Lentils and Broth: With your sautéed vegetables ready, it’s time to add those pre-rinsed lentils into the pot along with four cups of vegetable broth. Stir everything together gently so that all ingredients combine well before bringing this mixture to a rolling boil over high heat.

Once boiling occurs reduce heat immediately down to low-medium; cover partially with lid leaving it slightly ajar so steam can escape while allowing gentle simmering action—this should take approximately 30-35 minutes until lentils are tender yet firm enough not to fall apart completely!

Step Four : Season Your Stew: After simmering time has elapsed check if lentils have become tender—you may want to taste test at this stage! If they’re done simply season generously with salt & pepper alongside cumin powder,paprika & thyme stirring again after each addition ensuring even distribution across entire pot—let simmer uncovered for an additional ten minutes allowing flavors meld beautifully!

While waiting prepare potatoes by peeling them before chopping them into uniform chunks which aids even cooking process later on!

Step Five : Make Your Creamy Mash: In another pot bring salted water into boil then carefully add diced potatoes allowing them cook until fork-tender—about fifteen minutes should suffice here! Drain water carefully post-cooking then return drained potatoes back into original pot adding either heavy cream/non-dairy alternative along with adequate butter/margarine if desired position over low heat mixing consistently until smooth & creamy finish achieved!

Combining these two parts now becomes necessary—ladle generous portions from steaming hot hearty lentil stew atop luscious creamy mash plates creating beautiful presentation alongside fresh herbs like parsley if preferred!