Mix on low speed until combined, then switch to a dough hook, increase the speed to medium, and beat until smooth, about 2 minutes. Increase the speed to medium-high and begin adding 4 Tbs. of the butter 1 Tbs. at a time, mixing well between additions. Continue to knead until the dough forms a slack ball (it will ride the dough hook, be tacky, and not slap the bottom of the bowl, but it should generally come together into a loose mass), 2 to 3 minutes. If the dough doesnt come together, continue kneading while adding up to 1/4 cup of the reserved bread flour, until it does. Grease a large bowl with 1/2 Tbs. of the remaining butter and transfer the dough to the bowl, turning it over in the bowl to coat with butter. Cover the bowl with a piece of plastic wrap or damp kitchen towel and place the bowl in a draft-free spot until the dough has doubled in size, about 1 hour. Line a rimmed baking sheet with parchment paper and grease the parchment paper with the remaining butter. Generously flour your work surface using the remaining 1/4 cup of bread flour (if you used the bread flour in the dough, dust your work surface with more bread flour). Turn the dough out onto the work surface and sprinkle the top with some flour. Use your hands to press and flatten it into a rectangle. Using a rolling pin, roll the dough into a 1/4-inch-thick strip that is about 24 inches long by about 6 inches wide. Starting with one of the long sides, roll the dough on top of itself, making a long, thin baguette-shaped length. Pinch the edge to the body of the dough to seal, turn the dough so it lies horizontally on your work surface, and gently roll it on your work surface to even out any bulges and create a somewhat consistent 1-1/2-inch-wide rope. Bring the two ends of the dough together and pinch them into one another to seal. Carefully transfer the dough oval or circle to the prepared sheet pan. Cover with a piece of plastic wrap or a damp kitchen towel and set in a warm, dry spot to rise until doubled, about 1 hour.