Classic American: Mainstream Bar & Grill, Waukesha WI

It was the last night for Friday Night Live in downtown Waukesha. We met up with a couple of people in the know, Jim and Jenny. Locals as they might be called.
We were to meet at the Mainstream Bar & Grill. Like usual, I went online before heading out for the night, to assure there might be a burger on their menu. Quite the list, actually. There is a "Build Your Own" offering but they suggest that if you "Don't feel like thinking? Select one of our best sellers to the right and relax we've done the work for you".
I am not a fan of the BYO. You may have caught that from other posts. I might be more of a strip back your best seller and call it BYO. I didn't ask them to remove anything. The list of toppings sounded just fine. No sauces, vegetables or other foods that shouldn't be on a burger.
My order, the "Classic American". American cheese, fried onions, pickle, mustard, ketchup, lettuce and tomato.
I asked for slight pink for doneness.
The burger arrived. 1/2 pound. Cooked perfect, just the smallest amount of pink. I had to cut it in half because it was super stacked with lettuce, tomato, onion and slathered with  mustard and ketchup. They don't mention what kind of bun they use but, it was delicious also. It may have actually "made" the burger because it had a sweet edge to it. Sweet and savory, good stuff.
First bite, I was in. Really tasty. A bit messy because they did load it with quite a bit of mustard, something that might normally bother me, not this time. It was actually sort of fun trying not to make a mess. I wasn't successful. It was probably a 5 napkin meal by the time I finished. Fries were the choice for sides.
It sounded like all the other choices made were just as good.
Prices were within the norm for most burgers. Just a reminder, this was a half pound.

The waitress was very present and made sure we were taken care of at all times and the place was hoping. We sat on the deck out back, partially because the music was a bit on the loud side in the bar area. There is plenty of ample seating both in and out.
So, ratings...
4.5 of 5
Price for the portion, overall flavor, service and Jack N Cokes for $5!
Sorry I didn't get any pics. I was hungry.