Preheat oven to 400°F. Grease a 8x8 in. casserole dish with softened butter our spray with nonstick cooking spray, set aside.

In a large sauce pan cook macaroni according to package directions, drain in colander and set aside.

In the same sauce pan, melt butter with olive oil over med heat. The olive oil helps prevent browning of the butter.

Stir in chopped onion and cook until translucent, stirring occasionally. About 2 minutes.

Add flour stirring with whisk constantly for about 2 minutes more (to cook flour).

Gradually pour in half and half, whisking constantly. Stir in salt, pepper and cayenne. Bring to a low boil and continue boiling for 2 minutes. Still whisking constantly. (Half and half makes the best creamy sauce in my opinion. You could use milk if you want, but then stand a bigger chance of the sauce "breaking").

Reduce heat and gently simmer (stirring constantly, you guessed it) for 10 minutes to thicken.

Add shredded cheese a handful at a time. Whisking to incorporate each addition. Simmer, stirring, an additional 5 minutes, or until all cheese is melted. Turn off heat.

Return macaroni to sauce pan and gently fold into cheese sauce. Adjust seasoning to taste. I usually need to add a little more salt once the pasta is added (up to another 1/2 tsp), and sometimes add extra cayenne if we want a little extra kick.

Transfer to casserole dish. Now is where you add the topping if you want a little crunch. In a small bowl toss panko breadcrumbs with olive oil to coat. Sprinkle over top of mac n cheese.

Bake, uncovered, 20 minutes or until top is golden brown and edges are bubbly.

Notes: It is important to use extra sharp cheddar (or a mixture of sharp, strong cheeses) in order to really taste the cheese. Milder cheeses are not strong enough to truly provide a rich, cheesy flavor. I like using Kraft Shredded Triple Cheddar with a touch of Philly. If I feel like shedding my own I will get a block of good quality Vermont extra sharp white cheddar. If you want it extra, super cheese add up to an extra cup of cheese to your sauce. It's ok. I won't tell. ;-)

Substitutions and mix-ins: you can sub 1/4 cup sliced leeks for the onion, or omit this ingredient completely (although I say keep it). Can also sub nutmeg for cayenne, these brighten all the flavors and bring it all together (i would not use both). For variations in flavor, mix in about 4 slices crispy, crumbled bacon or 1/2 cup frozen spinach, thawed and drained with all excess liquid squeezed out when you sure in pasta.