Preheat oven to 180°C.
Cook macaroni according to the package directions. Drain.
In a large saucepan, melt butter and whisk flour in until well combined. Cook for 1 minute.
Slowly pour the milk and cream over whisking continuously to avoid any lumps. Simmer until thickened, mixing regularly. Season and simmer for another 2 minutes.
Add the cheeses in and stir until melted and smooth.
In a separate bowl, beat the egg, add a little cheese sauce and whisk again. Add to the cheese sauce along with cooked pasta. Stir until the pasta is well coated in cheese sauce.
Transfer to your selected oven proof dish.
For the topping
Place crackers in a food processor and blitz to a fine crumb.
Add melted butter and mix until well combined.
Top your mac and cheese with the cracker crumbs and bake until golden and bubbly, about 20 minutes.
Serve hot as a side (or have it as is!).