Peel the potatoes and place them in a pan of salted water. Bring to the boil then lower the temperature and simmer for 10-15 minutes until the potatoes are soft. Drain and place into a large bowl.
Add the ricotta to the potatoes and mash to a smooth consistency. Stir through the grated mozzarella, gruyere and parsley. Season to taste with salt and pepper and mix well to combine. The mixture should now be a little sticky.
Roll the potato mixture into golf ball sized balls, approximately 40g each in weight. Place the balls onto tray lined with greaseproof paper, cover and place in the fridge for 30 minutes.
Meanwhile look out 3 bowls. Place the flour into one bowl and season with salt and pepper. In another bowl crack and whisk the egg. Finally add the panko breadcrumbs to the third bowl.
Take the potato balls out of the fridge and dip each first in the seasoned flour, then into the egg and finally roll them gently in the breadcrumbs. Place each croquette back on the tray and once all have been coated they can be covered and returned to the fridge until you are ready to cook.
Take each tomato and cut a cross through the skin at the bottom of each. Place the tomatoes in a large bowl and cover with boiling water. After 2 minutes drain off the water and peel and discard the skin from each tomato.
Place the tomato on a chopping board and cut into wedges, removing and discarding the seeds and the core as you go.
Place the remaining flesh into a medium saucepan over a low heat. Add the sugar to the pan and cook gently until the tomato has cooked down and you have a nice thick sauce. Blitz to a smooth puree with a stick blender. Season with salt and pepper to taste.
30 minutes before you are ready to serve remove the croquettes from the fridge and allow to come to room temperature.
Meanwhile pour the sunflower oil into a large saucepan and bring up to a heat of 180C.
While the oil is heating, gently warm the tomato sauce.
Once the oil is up to temperature gently place the croquettes into the hot oil one at a time! Do not overfill the pan, 4 croquettes at a time is sufficient.
Cook the croquettes until golden, approximately 3-4 minutes. Then remove and place on some kitchen paper to drain. Pop the croquettes into a warm oven until you have cooked the remaining balls.
Once ready to serve, spoon the tomato sauce onto the plate and place the croquettes on top. We also like to add a few drops of the basil oil to the plate. Serve immediately.
You can use a good vintage cheddar or parmesan in place of the gruyere cheese.Parsley is delicious in this dish as it adds a freshness to the croquettes however you can easily substitute with basil if you prefer.This is a great make ahead dish. Both the croquettes and tomato sauce can be made ahead of time and kept in the fridge, or indeed frozen until needed. If you want to freeze the croquettes do so after rolling them into potato balls, and before you breadcrumb them. When ready to cook remove from the freezer and allow to defrost thoroughly before coating in breadcrumbs and deep-frying.