Preheat the oven to 450 degrees F.
Combine the flour, sugar, baking powder and kosher salt in a large bowl and whisk together. Pour in the buttermilk and use a wooden spoon to stir into a thick dough without overworking it -- some dry spots are ok.
Pour the butter into an 8-by-8-inch baking pan. Scrape the dough into the pan and spread to the edges. Use a butter knife to slice the dough into 9 equal squares. Bake for 22 to 25 minutes until golden brown on top and a toothpick inserted in the center comes out clean.
Remove from the oven and drizzle the honey over the top. Sprinkle with sea salt and let cool in the pan for at least 10 minutes before slicing and serving with butter and jam.