To a large microwaveable bowl add cauliflower and enough water just to cover.
Microwave for about 10 minutes or until completely soft, then drain and set aside.
Meanwhile, heat a medium saute pan on medium high heat.
Add half the butter and allow to melt.
Add shallots and saute for about 5-7 minutes until translucent and soft.
Add the garlic and saute until fragrant about 30 seconds.
Add the flour to the pan and allow to cook about 2-3 minutes, stirring the pan often but being careful not to let the flour burn.
Add the broth, milk and thyme leaves and whisk to incorporate ingredients.
Lower the heat to medium and continue to whisk often and until mixture thickens about 8-10min.
Stir in the nutmeg and season with salt and pepper.
Allow sauce to cool slightly about 5 min.
Very carefully transfer the sauce to a blender along with the cooked cauliflower, parmesean cheese and remaining butter.
Blend until completely smooth and velvety.
Use immediately or store in an air tight container for up to 3-4 days.