Mix yeast into warm buttermilk and let stand until the yeast is foamy.
Melt the butter, then combine with flour, brown sugar, honey, salt and one egg in the bowl of a stand mixer. Once the yeast is foamy, add the buttermilk/yeast mixture, then mix using a stand mixer for ca. 15 minutes until a dough is formed.
Cover the mixer bowl with a towel or plastic wrap and let the dough rise in a warm spot for 30-45 minutes until it's doubled in size.
Turn out the dough onto a lightly floured surface and divide into six equal sized pieces. Form the pieces into disks about 6cm in diameter, then place on a parchment paper lined baking sheet and let rise again in warm place for another 30 minutes.
Preheat oven to 140C. Bake the rolls for 10 minutes until they've risen, then remove from oven. Turn oven up to 200C. While oven is heating up, whisk the second egg and brush onto buns. Sprinkle sesame seeds onto the buns, then bake for another 10 minutes or until golden brown.
Move baked buns onto a wire rack to cool before slicing and building your burger