I am a big time fan of the banana/bubblegum style Weissbier's. I can't stand the bitter, clovy, overhopped, and watery American wheats. They can be tricky to master, and there is a ton of conflicting (and some erroneous) information on the subject. After many years of researching and adjusting my own banana goals, here's what I found works.
60 to 65 % Wheat (I generally buy Great Western white wheat. Large kernels, mill's nicely without adjusting, good flavor).
35 to 40% German pilsner malt (or Belgian).
If you really want some oats or whatever, go for it, but it's not necessary.
Toss in a half pound of rice hulls for safety
Don't use crap domestic 2-row
60 minute boil is fine, go longer if you wish. No shorter, that pilsner malt will reek of DMS during the boil
No aroma hops. Keep the bittering hops (45 to 60 minutes) to less than 16 IBU's or a bit less. Something of the Nobel persuasion (Saaz, Sterling, Spalt, etc). Stronger or more aroma will knock out the ability to sense the banana.
If able, adjust mash pH for 5.4 to 5.5
Mash in at 131, hold for 10 minutes (protein)
Raise it to 145, hold for 30 minutes (maltose)
Raise it to 160, hold for 30 minutes (sacc)
WLP300 is basically W-68 so you are already on the banana side of the yeast spectrum. No need to under pitch, but if it makes you feel better, go for it.
Give it a week or so at 73F to 76F
Keg it up. Good and fizzy. Drink it fresh.
Try it. I actually have had people ask if I use bananas in the recipe (yuck, that couldn't end well)
