Pre-heat the oven to 190C/Gas Mark 5.
Boil the macaroni in a large saucepan of water until al dente (check packet for timings).
While the pasta is cooking, warm the milk and bay leaf on a low heat until just under boiling point. Remove from the heat and set aside for 10 minutes.
Melt the spread in a large saucepan and sprinkle over the flour. Stir with a wooden spoon over a medium heat and cook for 1-2 minutes.
Gradually pour in the milk and bay leaf, and whisk until there are no lumps. Simmer, stirring occasionally, until it thickens.
Drain the pasta and transfer it to a large bowl. Pour over the white sauce and remove the bay leaf. Stir in the ricotta and mustard until combined. Add the spinach leaves and stir through. Season well with black pepper.
Spoon the pasta into a large, shallow, ovenproof dish. Scatter the tomatoes, Parmesan and breadcrumbs over the top. Bake for 35-40 minutes or until golden.