Preheat the oven at 200℃. Break the cauliflower into florets and cut it into small slices.

Fill a pan with water and add a little bit of salt to it. Bring it to a boil and add cauliflower to it.

Cook the cauliflower for about 5 to 6 minutes. Then, take it out, shock it in ice water, and keep it aside.

In a pot, cook the macaroni al dente. Drain the water and set it aside.

Take a bowl and add the cooked macaroni and cauliflower to it.

Add about four tablespoons of butter to it and mix them well.

Then, place a saucepan on the heat and melt the remaining butter in it.

Add flour and mustard powder to it and keep stirring.

Then, slowly pour in milk while stirring so no lumps are formed.

Lower the flame and keep stirring the roux until it thickens.

Also, season it with salt and some cayenne pepper.

Mix the three kinds of cheese in a bowl. Add half of that to the roux and keep stirring until smooth.

Then, add the macaroni and cauliflower mixture to the saucepan and mix it to cover it with the roux.

Now, take a baking dish and put this macaroni mixture in it. Top with the remaining cheese, breadcrumbs, and thyme leaves.

Place the baking dish in the oven and cook it for about 15-20 minutes. Take it out when the top looks golden and crispy and then, serve it.