Stir the warm water and honey in a small bowl until dissolved, then stir in the yeast; set aside until creamy or foamy, about 5 minutes. Meanwhile, whisk the flour, baking powder, baking soda and kosher salt in a large bowl.
Add the cut-up butter to the flour mixture and work it in with your fingertips until the butter is in pea-size pieces. Make a well in the center and add the yeast mixture and buttermilk. Stir with a wooden spoon or rubber spatula until the flour is completely moistened and the dough looks like a shaggy ball. Cover the bowl with plastic wrap and let rise at room temperature until the dough is doubled in size, 1 to 1 1/2 hours.
Lightly brush the bottom and sides of a 9-inch pie plate or 9- to 10-inch cast-iron skillet with melted butter. Turn out the dough onto a lightly floured surface and briefly knead three or four times until smooth. Pat until 1 inch thick; fold in half like a book and pat to 1 inch thick again. Rotate the dough 90 degrees and repeat folding and patting two more times. Cut out rounds using a 2 1/4-inch biscuit cutter (dip the cutter in flour if the dough is sticky). Gently knead the scraps together once to cut out more biscuits. You should have about 10. Place them close together in the pan. Cover and refrigerate until the biscuits rise and are cold and firm, at least 3 hours or overnight.
Preheat the oven to 425˚ F. Brush the tops of the biscuits generously with melted butter. Bake until browned on top and firm in the spots where the biscuits meet, 20 to 25 minutes. Brush again with more melted butter and sprinkle with flaky salt. Let cool in the pan for at least 20 minutes, then slide out.