Heat the butter and rosemary in a small saucepan until the butter browns and the solids separate, about 8-10 minutes. Pour into a tempered, airtight jar and set in the freezer until firm, about 15 minutes.
When the butter is ready, prepare the biscuits. Whisk together flour, baking powder, and salt. Cut the browned butter-rosemary mixture into the flour with a pastry cutter, two forks, or your fingers, until pieces no larger than a pea remain and the mixture is crumbly. Slowly stream in the buttermilk, stirring until a shaggy but cohesive dough forms.
Dump dough onto a lightly floured surface and form into a 6 x 6 inch square. Cut into four slices and stack atop one another, then press down until about 2 inches thick. Roll or press the dough into a 1-inch thick rectangle. Slice 9 biscuits out of the dough. Lay parchment onto a baking sheet and set the biscuits atop. Place in the freezer for 15 minutes to set.
Preheat the oven to 400 degrees. Remove the biscuits from the freezer, brush with buttermilk, and bake for 20-22 minutes until golden and risen.
For the maple whip, beat the heavy cream, maple syrup, bourbon, and salt until firm peaks form. Serve the biscuits with the whip and some apple butter or another jam/spread.