• Preheat the oven to 180 degrees Celsius

Tuna and vegetable filling

• Heat the oil in a large saucepan.
• Add both onions and fry until glassy, ​​about 3 minutes.
• Then add the leek and garlic and stir-fry everything for 1 minute.
• Spoon the flour through the vegetables and fry for 3 minutes. Make sure you do that otherwise you will taste the flour.
• Pour the stock into the vegetables and stir well. Then add the carrot, celery, wine and thyme.
• Let simmer for 5 minutes.
• Finally add the milk and tuna to the skillet and season with salt and pepper.
• Bring to the boil and turn off the heat.
• Put the tuna vegetable filling at the bottom of the baking dish.

Mashed potatoes (can be prepared at the same time as the tuna vegetable filling)

• Peel the potatoes and cut them in four (if they are large).
• Put them in a pan with water. Make sure the waterlevel is about 0.5 cm above the potatoes.
• Bring the water to the boil and boil the potatoes until they are tender (you can then easily prick the potato with a fork and feel no resistance).
• Drain the potatoes and mash them.
• Heat the milk with the herb butter in a pan until the herb butter has melted.
• Pour with the mashed potatoes and mix everything well.
• Spoon the mashed potatoes on the tuna vegetable filling.

Topping

• Mix the cheddar with the panko and thyme in a small bowl.
• Sprinkle that over the potato in the casserole.
• Place the baking dish in the oven and bake for 20 minutes until the cheese is melted and golden brown.