Step 1

Preheat oven to 350F. Line an 8-by-8-inch baking pan with aluminum foil, spray with cooking spray; set aside.

Step 2

In a large, microwave-safe bowl add the white chocolate, butter, and heat to melt, about 2 minutes on high power. Stop to check and stir after 1 minute, and then heat in 20-second bursts, stopping to stir after each burst, until mixture can be stirred smooth. White chocolate is very prone to scorching and seizing up, so watch it carefully and don’t overheat.

Step 3

Wait momentarily before adding the egg so you don’t scramble it. Add the egg, sugar, vanilla, and whisk until combined.

Step 4

Stir in the bananas until well-combined.

Step 5

Add the flour, optional salt, and stir until just combined; don’t overmix.

Step 6

Turn batter out into prepared pan, smoothing the top lightly with a spatula.

Step 7

Bake for about 32 to 33 minutes, or until a toothpick inserted in the center comes out mostly clean, or with a few moist crumbs, but no batter. In the last 15 minutes of baking, make the glaze.

Step 8

Brown the butter (click for tutorial). Cook butter over medium-high heat in a small saucepan until it’s amber to brown in color, about 5 minutes depending on pan size, but watch it closely so you don’t burn it. I swirl the pan in the last minute or so to make sure I can really see the color changes. Butter will go through stages of hissing, sputtering, and making noise until the water cooks off at which point the browning occurs. Butter will smell nutty and aromatic.

Step 9

Transfer butter, including brown bits at the bottom of the pan (they’re flavor powerhouses, keep them) from pan to large mixing bowl which stops any carryover cooking.

Step 10

Add the confectioners’ sugar, vanilla bean paste, optional salt, and slowly add the milk, whisking until smooth or beat with a handheld electric mixer. As necessary, add additional cream (or confectioners’ sugar) to reach desired glaze consistency. Glaze should be of medium thickness and easily pourable.

Step 11

Evenly pour glaze over bars (they don’t have to be cooled first), smoothing it lightly with a spatula if necessary, but glaze will likely just slide into place.

Step 12

Allow bars to cool in pan uncovered for at least 2 to 3 hours, (or overnight and cover with a sheet of foil) before slicing and serving so glaze can set up.

Step 13

Bars will keep airtight at room temperature for up to 1 week, or in the freezer for up to 6 months.