Directions Prep:20min › Cook:35min › Extra time:10min › Ready in:1hr5min
Preheat oven to 190°C. Lightly coat a 33 x 22 x 5 cm baking dish with non-stick cooking spray.
Cook macaroni in a large saucepan of lightly salted boiling water until al dente, following packet instructions. Drain well; return to pan.
Heat oil in a large non-stick saucepan over medium heat. Add the spring onion and salt. Cook, stirring occasionally, for 3 minutes. Gradually stir in flour. Cook 1 minute.
Gradually stir in 1 cup of milk until thoroughly blended. Stir in the remaining milk. Bring to the boil. Lower heat and simmer, stirring, until lightly thickened, 2 to 3 minutes. Remove from heat. Stir in mustard, cheddar and half the parmesan.
Fold sauce into the macaroni. Transfer mixture to baking dish. Place the tomatoes in single layer over the top. Combine remaining parmesan and breadcrumbs; sprinkle over tomatoes.
Bake until the filling is bubbling and the topping is lightly browned, about 20 minutes. Let stand 10 minutes; serve.