In a bowl, combine 6 tbsp lukewarm milk, 2 tsp Saf-Instant Yeast, and 2/3 cup flour. Cover and let it rest for 2-3 hours, or overnight in the fridge for maximum flavor.

Into the poolish, add 1 cup milk, 3 cups King Arthur Bread Flour, 3.5 tbsp sugar, 2.5 tsp salt, 0.5 tbsp vanilla extract, and 1/2 tbsp softened butter. Stir until incorporated, let it rest for about 30 minutes, then knead until smooth and elastic (5-10 minutes). Let it rise until doubled in size, approximately 1-2 hours.

While your dough rises, beat the chilled butter (22 tbsp) with a rolling pin between parchment paper until it spreads out into a rectangle. Chill again to keep cold.

Roll your risen dough into a rectangle large enough to encase the butter block. Layer the butter, fold the dough like a book, and roll out again. Repeat the folding and rolling process 3-4 times, chilling for 30 minutes between each round.

In a bowl, mix together 1/2 cup granulated sugar, 1/4 cup brown sugar, 1 tbsp freshly grated orange zest, 1.5 tsp ground cinnamon, and 1/4 tsp salt.

Roll out the dough into a large rectangle, brush with 3 tbsp of melted butter, and sprinkle the filling evenly. Roll into a log, cut sections, and place in a muffin tin to rise for about 30 minutes.

Preheat your oven to 375°F (190°C). Bake the buns for 45-60 minutes or until golden brown on top. Let cool upside down for a few minutes before serving.