Cook the macaroni in a large saucepan of lightly salted boiling water for 8–10 minutes, or according to the packet instructions, until al dente.
Add the spinach to the pan and cook for 1 minute until wilted. Drain well and place in a 1.5 litre (2½ pint) ovenproof dish.
Meanwhile, place the butter, flour and milk in a saucepan and whisk constantly over a medium heat until the sauce boils and thickens. Simmer for 2–3 minutes until you have a smooth glossy sauce, then reduce the heat to low and stir in the Taleggio or fontina and mustards. Season to taste with salt and pepper and cook gently until the cheese has melted.
Pour the sauce over the macaroni and spinach, scatter over the tomatoes and then sprinkle with the breadcrumbs and Cheddar.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 20 minutes until golden and bubbling.