Procedure:

1) Place the White Lightning blend in the bowl of a stand mixer. Place the buttermilk into the microwave-proof measure and heat in the microwave for 20 seconds on high, or until temperature is 80 F. Add the sourdough starter and egg to the buttermilk and whisk to blend. Add liquids to the flour and mix on low until all flour is wet. Let dough rest 5 minutes, then mix on medium-high for one minute. Transfer dough to a large bowl, shaping into a ball. Cover bowl with kitchen towel and allow to rise, 4 hours at 72 F.

2) Meanwhile, bring 3 Tablespoons of the butter to room temperature. Line the quarter-size sheet pan with bakers parchment. Optional: grease the steamer insert with butter and dust lightly with potato starch. Liberally dust the work surface, rolling pin, bench knife, offset frosting spatula and ruler with potato starch.

3) 30 minutes before dough is finished rising, remove 8 Tablespoons (1 stick) butter from refrigeration and place on the work surface, standing on end. (This prevents it from becoming too soft, too soon.)

4) Return dough to stand mixer bowl. Add the sugar and yeast and beat on medium high for about 2 minutes, until these dry ingredients are integrated. With mixer running, carefully add the 3 Tablespoons softened butter, in chunks. Mix another minute at medium high speed until butter is thoroughly integrated.

5) Turn dough out onto the well-dusted work surface. Dust the top of the dough and your hands, then pat and shape the dough into a rough block, about 6 inches long X 3 inches thick X 3 inches wide. Slide the offset spatula underneath the block to assure it is not sticking to the work surface, then slide the block off to a side.

6) Place the unwrapped stick of butter onto a piece of bakers parchment. Dust the butter on all sides with potato starch. Use the rolling pin as a hammer to gently tap the butter, working to flatten it into a consistent rectangle. You will need to turn the stick over occasionally to avoid it sticking to the parchment. When butter is about 3/4" thick, roll with the rolling pin to achieve a long rectangle about 4 1/2 inches wide and 3/8 inches thick. Set butter aside.

7) Bring the dough block back to the center of the work surface. Using the bench knife, ruler, and offset spatula to maintain straight edges, roll the dough into a slab that is 10 inches long, 4 1/2 inches wide, and about 3/4 inches thick, dusting as needed to prevent sticking. Run the spatula under the slab from time to time to assure dough is not sticking.

8) Divide the dough into thirds, cutting straight down with the bench knife. Do not brush potato starch away. Measure the center portion and cut a slab of butter that will fit exactly. Place the butter on the center portion of dough. Place one of the end portions atop the butter, Measure the end portion and cut a slab of butter to fit. Place butter on dough and top with the final end portion. Cover this stack with a kitchen towel and allow to rest 15 minutes.

9) Rolling gently, and keeping dough edges straight with the bench knife, ruler and offset spatula, roll the dough and butter "stack" out to a 10-inch X 5 inch rectangle. Take care to assure the butter maintains the same size as the dough. Mark the 10-inch dimension in thirds, then gently fold dough "business letter style", ending with a stack that is about 3 1/2 inches long X 5 inches wide.

10) Turn dough stack 90 degrees and gently roll into a slab that is about 4 inches wide and 12 inches long, taking care to keep butter in the same shape as the dough.  Use the bench knife to divide the dough into 4 pieces, each 3 inches wide and 4 inches long. Place 3 meltable chocolate ovals at the edge of each rectangle, then loosely roll the dough over the chocolate, ending with the seam side down. Transfer the rolls to the prepared sheet pan. Optional: Transfer rolls to prepared steamer insert. See note, below. Cover loosely with a kitchen towel or piece of plastic wrap and allow proof 1 hour at 72 F.

11) Heat oven to 425 F. Place the second egg in the small bowl and whisk to mix. Use the dry pastry brush to gently remove potato starch from the rolls, then brush each roll with the egg wash. Bake for 20 - 30 minutes, or until surface is nut-brown and chocolate has begun to melt and ooze out. Remove to a cooling rack and allow to reach a safe temperature before eating.

Note: The steamer insert provides better baking and lift to the bottom layers of the rolls. The insert is a round, multi-leaf, perforated, stainless-steel product designed to unfold in a large saucepan for steaming vegetables. The center post is easily removed; the leaves will unfold almost flat. Because butter will drip through the perforations the steamer must be placed on a sheet pan to use.

Rolls are best eaten within 8 hours of baking. They may be frozen and re-heated.