Potato & Onion Bake in a Mornay Sauce

For the Mornay Sauce
Heat your butter in a large pot over medium heat
Once melted, reduce the heat to low and slowly whisk in the flour – one tablespoon at a time
After the flour is incorporated, the roux should be thick. Pour in half the coconut milk and whisk to combine. Once combined, add the rest of the coconut milk
Fold in half the cheese and stir until incorporated into the béchamel sauce
Then, fold in the rest of the cheese
Whisk in the spices, then remove from heat
For the Potatoes
Preheat your oven to 375 degrees Fahrenheit and spray a 9″ by 13″ baking dish with nonstick spray
Wash and peel the potatoes, then use a mandolin to slice the potatoes into 1/2″ thick pieces
Next,  julienne your white onion and set to the side
Begin layering the potatoes on the bottom of the dish, laying against one another and making three to four rows along the dish
After the first layer of potatoes is down, add 5-10 pieces of the julienned onion
Then pour a little less than one fourth of the mornay sauce over the potatoes and onions. Use a spatula to spread the sauce over the vegetables.
Repeat for the next three layers
Once the final layer is finished, sprinkle the gruyere and parmesan cheeses over the top
Place the butter squares along the four edges of the baking dish and place one square in the middle
Cover with aluminum foil, and bake for 75 minutes
Remove the foil, and bake for another 15 minutes until the cheese is bubbling
Finally, broil on high for 5 minutes until golden brown 
Allow to cool for 20 minutes then finish with freshly minced parsley