Grease a baking dish with oil. Cook the pasta in lightly salted boiling water according to package instructions. Drain and return to the warm pot.
In a large saucepan, melt butter over medium heat, add onion and cook for 2-3 minutes.
Now, stir in flour, salt, and black pepper, and add milk (whisking constantly) until thickened. Then remove from heat.
Add mozzarella cheese, cheddar cheese, Gouda cheese, and half of the Parmesan cheese, whisking until cheeses are melted and the sauce is smooth.
Now, pour the cheese sauce over the cooked pasta; stir to coat. Transfer the mixture to the baking dish.
In a microwave-safe bowl, melt the 1 teaspoon butter, then stir in panko and the remaining Parmesan cheese and sprinkle the mixture over the pasta.
Bake for 5-10 minutes or until the top is browned. Garnish with parsley and serve.
Notes
When taking the saucepan off the heat to add the cheese, go slow with the process. Add the one cheese and let it dissolve into the sauce before adding the next. It's also a good idea to cut them into chunks to melt faster.