Heat sunflower oil in a heavy-based pot. Sauté onions until soft, then add pork pieces, browning them while seasoning with salt, black pepper, and celery salt.
Incorporate the carrots, beer, and stock, bringing to a simmer for 20 minutes. Thicken the stew with the cornflour mixture, then add milk, simmering for an additional 10 minutes.
Stir in the spinach, remove from heat, adjust seasoning to taste, and serve with maize meal and bread.
This stew is not just a meal but a comforting experience, bringing together the robust flavours of pork, the heartiness of vegetables, and the distinctive taste of beer in a deliciously thick sauce.