Preheat the oven to 180C/350F/Gas 4.
For the roulade, whisk the egg whites and lemon juice in a large clean bowl until stiff peaks form when the whisk is removed.
In a separate bowl, mix together the cornflour, milk, mustard, salt and freshly ground black pepper and egg yolks until well combined. Fold this mixture carefully into the whisked egg whites.
Line a baking tray with silicone paper and pour the mixture onto the tray, spreading it into the corners. Transfer to the oven to cook until set and golden-brown, about 5-8 minutes.
Heat the olive oil in a pan and cook the spinach for a minute or two, stirring until wilted. Stir in the chopped tomato and the mozzarella.
Remove the roulade from the oven and spread over the wilted spinach, tomato and mozzarella. Using the silicone paper to help, roll up the roulade into a log.
For the spicy tomato sauce, heat the oil in a saucepan and fry the onion until translucent, about 4-5 minutes.
Add the tomato, chilli flakes, red wine and sugar and simmer the sauce for five minutes until slightly reduced. Stir in the butter and the chopped fresh mint.
To serve, slice the roulade and arrange on two serving plates. Garnish with the spinach leaves and pour over the spicy tomato sauce.