Preheat the oven to 350°F.
Cover the bottom and sides of a 9x13'' pan with parchment paper.
If using walnuts, place on a baking sheet in a single layer and toast until golden in the preheated oven, about 10 minutes.
Slice the butter into 15-20 pieces, place in a heavy-bottomed saucepan over medium heat and stir constantly until melted. As it melts, the butter will foam. Keep cooking the butter after the foam subsides for another 7-10 minutes, continuing to stir occasionally. It is done once the milk solids turn golden brown and the butter takes on a nutty fragrance. Remove from the heat, pour into a heat-safe bowl to cool slightly.
Pit and dice the dates and dried cherries into bite-sized pieces.
Meanwhile, cream together sugar, eggs, vanilla, bourbon, and salt. Mix until combined.
Whisk in the browned butter.
In a separate bowl, stir together flour and baking powder. Fold the flour mixture into the wet ingredients.
Be sure the dough is no warmer than room temperature, then gently fold in dates, dried cherries, and chocolate chunks (and walnuts, if using).
Dollop the sticky, thick dough in to prepared pan and gently even out the top, pushing the dough into the corners. Bake for 25-35 minutes, until shiny golden brown and slightly cracked on top and a toothpick comes out with crumbs attached.
Allow to cool in pan for at least 10 minutes, then transfer to a metal cooling rack until completely cool.
I think these are even better one day after baking, if you can wait that long. They will keep in an airtight container at room temperature for 4 days, or you can cut in blondies into squares, then freeze for up to one month.