Heat the oil in a large saucepan over medium-heat. Add the onion and fry until soft and transparent the add the garlic and fry until soft and fragrant. Add the mushrooms and fry, stirring occasionally, until browned. Add the celery and carrots and fry, stirring occasionally, until soft.
While the vegetables are cooking, cook the potatoes. You can peel, cube and boil them or you can leave them whole and unpeeled, pricked all over with a fork, and put them in the microwave. Microwave on high for 5 minutes, then flip and microwave for an additional 5 minutes. If they still cannot be easily pierced with a knife, continue microwaving in 2 minute intervals. Remove and let cool for a few minutes until you can peel the skin off but the potatoes are still warm.
Transfer the cooked potatoes to a bowl and mash. Add in 2 tablespoons of butter/oil and 2 tablespoons of cream/milk. Taste and add additional butter and/or milk if you think it’s necessary. Season with salt.
Preheat the oven to 400 F / 200 C.
Back to the filling. When the veggies are tender, add in your favourite herb. Sprinkle over the flour and cook, stirring continuously, for 2 – 3 minutes to cook out the raw flour taste. Pour in the wine and stock and bring to a simmer while stirring constantly. Simmer for 2 – 3 minutes or until thickened.
Add the beans and cream. Season with salt and pepper to taste. Remove from the heat and divide the filling between your baking dishes or ramekins.
If you want to make it fancy, transfer the mashed potatoes to a piping bag and pipe over the filling. I did it in a wavy, back and forth motion. You can also spoon the potatoes overtop, then run a for over them to create lots of peaks and valley which will crisp in the oven.
Bake for 30 minutes or until the mashed potatoes are golden brown and crispy on their peaks and the filling is bubbling. If it’s taking too long you can pop them under the broiler for a couple of minutes, watching carefully.