Make the dough: In the bowl of a stand mixer fitted with the paddle attachment, beat 1 1/2 cups (188g) flour, salt, caraway seeds, yeast, sesame seeds, and onion powder at low speed until well combined.
In a small microwave-safe liquid-measuring cup, heat lager on high in 10- to 15-second intervals until an instant-read thermometer registers 120°F (49°C) to 130°F (54°C). Add warm lager, melted butter, and honey to flour mixture; beat at medium speed until combined. Add egg; beat until combined. With mixer on low speed, gradually add 2 cups (250g) flour, beating just until combined and stopping to scrape sides of bowl.
Switch to the dough hook attachment. Beat at low speed until a soft, somewhat sticky dough forms, 8 to 10 minutes, stopping to scrape sides of bowl and dough hook; add up to remaining 1/4 cup (31g) flour, 1 tablespoon (8g) at a time, if dough is too sticky. (Dough should pass the window pane test [see Notes] but may still stick slightly to sides and bottom of bowl.) Turn out dough onto a very lightly floured surface, and shape into a smooth round.
Lightly oil a large bowl. Place dough in bowl, turning to grease top. Cover and let rise in a warm, draft-free place (75°F/24°C) until doubled in size, 40 to 50 minutes.
Spray a 12-cup muffin pan with cooking spray.
Punch down dough; cover and let stand for 10 minutes. Turn out dough onto a clean surface, and divide into 12 portions (about 72g each). Divide each portion into 3 pieces (about 24g each). Roll each piece into a smooth ball, pinching closed any seams. Place 3 doughballs, seam side down, in each prepared muffin cup. Cover and let rise in a warm, draft-free place (75°F/24°C) until puffed and dough holds an indentation when poked, 20 to 30 minutes.
Preheat oven to 400°F (200°C).
Make egg wash: In a small bowl, whisk together 1 tablespoon (15g) water and 1 egg (50g). Brush rolls with egg wash.
Bake until golden brown and an instant-read thermometer inserted in center registers 190°F (88°C), 8 to 10 minutes, rotating pan halfway through baking. Gently brush tops of rolls with melted butter; garnish with caraway seeds and sesame seeds, if desired. Serve warm or at room temperature. Store in an airtight container for up to 4 days.