Sauté the vegetables: Heat 1 tablespoon of oil in a large pot over medium heat. Incorporate the chopped onion and minced garlic, sautéing until they become tender and aromatic, which should take around 3 to 4 minutes.

Add the veggies: Toss in the chopped broccoli and frozen vegetable mix (peas, sweetcorn, carrots, and green beans). Stir well and cook for another 5 minutes, allowing the vegetables to thaw and slightly soften.

Pour in the stock: Add the vegetable stock to the pot, along with the dried oregano, bay leaves, and a pinch of black pepper. Stir everything together, bring to a gentle boil, then reduce the heat and let the soup simmer for about 10 minutes, allowing the flavors to meld.

Make the roux: In a separate small saucepan, melt the butter over medium heat. Stir in the flour and cook for 1-2 minutes, stirring continuously to form a roux (a smooth paste). Gradually whisk in the milk and continue stirring until the mixture thickens and becomes creamy.

Combine everything: Slowly add the milk mixture to the simmering vegetables, stirring continuously to ensure everything blends smoothly. Mix in the mustard and stir thoroughly to blend it in completely. Let the soup simmer for an additional 5-7 minutes until it thickens to your desired consistency.

Final touches: Remove the bay leaves, give the soup a final stir, and adjust seasoning with more black pepper if needed.

Serve: Ladle the creamy veggie pot pie soup into bowls and enjoy with crusty bread or biscuits for a complete, comforting meal.