Slice potatoes to about 3 mm thick. It’s important to keep the slices thin to ensure they cook through in the oven. The thicker the slices are, the longer they will need to bake in the oven.
Layer and spread out the potato slices into a medium baking dish.
In a small pot on medium to high heat, add the butter and melt.
Add garlic and cook until it just starts to brown (about 45 seconds).
Add plain flour and stir until there are no lumps.
Add milk and thickened cream gradually while stirring until the mixture is fully combined and smooth.
Bring to boil then remove from heat.
Pour the sauce over the top of the potatoes in the baking dish.
Sprinkle the potatoes with parmesan.
Cover with foil and bake for 45 minutes.
Remove foil from baking dish and bake for a further 30 minutes, until the top is golden brown. Check the potatoes are cooked through by inserting a skewer into the potatoes. Return to oven and bake longer if necessary.
Remove from oven and garnish with parsley, then serve.