Fill a large casserole pan with water ⅔ of the way up. Add a few big pinches of salt and bring to a boil. When the water is boiling add the pasta and stir. Boil the pasta until soft and al dente. Once cooked, carefully strain into a colander and return to the pan.

While the pasta is cooking, add the butter to a large, shallow casserole pan on a medium heat. Once melted, add the onions and sauté until translucent. Add the minced garlic and sauté until fragrant.

Add the flour to the pan and stir to combine with the melted butter, onions and garlic. Pour in a third of the milk and whisk straight away. Add another third and whisk and then the final third and whisk until there are no lumps. As the sauce starts to thicken, add the chicken stock and continue stirring until smooth and creamy with no lumps. The mixture should be thick enough to coat the back of a wooden spoon.

Add the wholegrain mustard, Dijon mustard, dried thyme, salt and pepper to the sauce and stir to combine. Add the baby spinach and stir through to wilt the spinach. Once the spinach is wilted, turn off the heat.

Add the shredded chicken and broccoli to the pan and toss through the sauce until well combined.