Whisk the warm buttermilk, warm water, yeast, and 2 Tablespoons sugar together in the bowl of your stand mixer fitted with a dough hook or paddle attachment. Cover and allow to sit for 5 minutes or until foamy on top.

Add the remaining sugar, the butter, egg, salt, and 1 cup flour. Beat on low speed for 30 seconds, scrape down the sides of the bowl with a silicone spatula, then add the remaining flour. Beat on low speed until the dough comes together and pulls away from the sides of the bowl, about 2 minutes. *If you do not own a mixer, you can mix this dough with a large wooden spoon or silicone spatula. It will take a bit of arm muscle.*

Keep the dough in the mixer (and switch to the dough hook if using the paddle) and beat for an additional 5 full minutes, or knead by hand on a lightly floured surface for 5 full minutes. (If you’re new to bread-baking, my How to Knead Dough video tutorial can help here.) If the dough becomes too sticky during the kneading process, sprinkle 1 teaspoon of flour at a time on the dough or on the work surface/in the bowl to make a soft, slightly tacky dough. Do not add more flour than you need because you do not want a dry dough. After kneading, the dough should still feel a little soft. Poke it with your finger—if it slowly bounces back, your dough is ready to rise. You can also do a “windowpane test” to see if your dough has been kneaded long enough: tear off a small (roughly golfball-size) piece of dough and gently stretch it out until it’s thin enough for light to pass through it. Hold it up to a window or light. Does light pass through the stretched dough without the dough tearing first? If so, your dough has been kneaded long enough and is ready to rise. If not, keep kneading until it passes the windowpane test.

Lightly grease a large bowl with oil or nonstick spray. Place the dough in the bowl, turning it to coat all sides in the oil. Cover the bowl with aluminum foil, plastic wrap, or a clean kitchen towel. Allow the dough to rise in a relatively warm environment for 1.5-2 hours or until double in size. (I always let it rise on the counter. Takes about 2 hours. For a tiny reduction in rise time, see my answer to Where Should Dough Rise? in my Baking with Yeast Guide.)

Grease a 9×5-inch loaf pan.

Punch down the dough to release the air. Place dough on a lightly floured work surface and with a floured rolling pin, roll the dough out into a 9×15 inch rectangle (approximately).

Spread softened butter all over the top of the dough, leaving a 1/2 inch border uncovered. The softer the butter is, the easier it is to spread in this step. (Microwave it for a few seconds to soften if needed.) Mix the brown sugar and cinnamon together, then sprinkle evenly all over the butter.

If you need a visual, watch the video to see exactly how I do this step. Tightly roll the dough into a 15-inch log. Place the log on its seam. Using a sharp knife, cut the log in half lengthwise. I find a serrated knife works best. Criss-cross one half on top of the other half—forming an X. Tightly twist the two together. Pinch the outer edges to seal as best you can. Place in prepared loaf pan and cover with aluminum foil, plastic wrap, or a clean kitchen towel. (This step can get a little messy!) Allow the covered loaf to rest for 30 minutes. It will slightly rise during this time.

Adjust the oven rack to the lower third position. Place a baking sheet on the lower rack to catch any cinnamon/sugar that may drip down. Preheat the oven to 350°F (177°C).

Whisk the melted butter, brown sugar, cinnamon, and flour together. Spoon over loaf right before baking.

Bake until golden brown and, when gently tapped, the top of the loaf sounds hollow, about 45-55 minutes. The top browns quickly as it bakes, so tent the entire loaf with aluminum foil. (I usually place foil on top after about 20 minutes.) Remove finished bread the oven and place on a wire rack. Cool for 10 minutes in the pan, then remove from the pan and cool loaf on the wire rack.

Slice and serve warm or at room temperature. Cover and store leftovers at room temperature for 2 days or in the refrigerator for up to 1 week. Leftover slices taste delicious when warmed in the microwave for 10 seconds. Topping tends to lose its crunch after a day or 2.