Whisk flour, yeast, and salt together in bowl of stand mixer. Whisk water, oil, 1 egg (50g), and honey in 4-cup liquid measuring cup until sugar has dissolved.
Using dough hook on low speed, slowly add water mixture to flour mixture and mix until cohesive dough starts to form and no dry flour remains, about 2 minutes, scraping down bowl as needed.
Increase speed to medium-low and knead until dough is smooth and elastic and clears sides of bowl but sticks to bottom, 8–12 minutes. Add butter, 1 tablespoon at a time, until thoroughly incorporated, 2–4 minutes.
Transfer dough to lightly floured counter and knead by hand to form smooth, round ball, about 30 seconds. Place dough seam side down in a large lightly greased bowl or container; cover with clean kitchen towel or plastic wrap, and let rise until doubled in size, 1–1½ hours.
Line 2 rimmed baking sheets with parchment paper. Gently punch dough down. Transfer dough to clean counter.
Press and stretch dough into 12×6-inch rectangle, with long side parallel to counter’s edge. Using a knife, cut dough in half horizontally (parallel to you). Then cut 6 even vertical cuts to form 12 identical pieces. Cover pieces with towel.
Lightly dust half of work surface with flour. Lightly dust hands, then working with 1 piece of dough at a time (keep remaining pieces covered), stretch and roll into 14-inch rope on undusted half of work space.
Lightly roll rope through flour, then shape rope into U with 2-inch-wide bottom curve and ends facing away from you.
Tie ends into single overhand knot, with 1½-inch open loop at bottom.
Wrap 1 tail over loop and press through opening from top.
Wrap other tail under loop and pinch ends together to seal.
Arrange rolls pinched side down on prepared sheets, spaced evenly apart. Cover loosely with towel and let rise until nearly doubled in size and dough springs back when poked gently with knuckle, 30–60 minutes
In a small bowl, combine poppy seeds, sesame seeds and flaky sea salt.
Heat oven to 350ºF (176ºC) with racks set in upper-middle and lower-middle positions. Lightly beat remaining egg with 1 teaspoon water, then gently brush rolls with egg mixture and sprinkle with seed mixture, if using.
Bake until golden brown, 25–30 minutes, switching and rotating sheets halfway through baking.
Transfer rolls to wire rack and let cool completely, about 1 hour, before serving.