Before you do anything set the oven to 350 F.

Grease a large casserole dish.

Place a large saucepan on medium heat.

Add the onion, garlic, and thyme then cook them for 4 min.

Add the flour, salt, and black pepper then mix them.

Add the milk gradually with cream while whisking all the time.

Cook the mix until it starts boiling.

Cook them for 2 min on low heat.

Add the cheese with sour cream and combine them until they melt.

Lay half of the sliced potato in the greased casserole dish.

Pour half of the onion mix on it.

Repeat the process to make another layer.

Sprinkle the breadcrumbs on top.

Cook it in the oven for 1 h 12 min.

Serve it warm.