Caramelizing The Onion
Heat butter and olive oil in a large skillet
Add onions, salt, and pepper
Stir constantly until onions begin to soften (about 5 min)
Add sugar
Cook until golden brown (about 20 min), stir frequently

Preheat oven to 350°F

Add pasta to a large pot of salted boiling water, cook until al dente (about 10 min)

Meanwhile, melt butter in a large saucepan over med. heat

Add flour, stir constantly for 3 minutes

Heat milk in the microwave

Stir in hot milk, 1/4 cup at a time. Continue until it comes to a simmer

Remove from heat and add most of the cheese (at least 3/4 of it), stir until melted

Add salt and pepper

Combine caramelized onions, pasta, and cheese sauce to a greased 9x13 backing dish

Sprinkle the remaining cheese on top

Bake until golden and bubbling, about 40 minutes