Can I use bottled lemon juice?
Fresh is the move here. Bottled juice can taste flat or slightly metallic. If bottled is all you have, use it in the batter, but still try to use fresh zest. Zest is where the magic lives.
Why rub zest into sugar?
Lemon zest contains aromatic oils. Rubbing it into sugar crushes and distributes those oils so the lemon flavor is stronger and more even. It is a tiny step that makes a big difference.
Can I make this in a Bundt pan or as a layer cake?
Yes. For a 10 to 12-cup Bundt, bake at the same temperature and start checking around 45 minutes. Most will land in the 45 to 60+ minute range depending on your pan and oven. For two 8-inch layers, divide the same batter evenly between pans and start checking around 22 to 30 minutes. In both cases, use the same doneness cues: golden top, a tester with moist crumbs, and a gentle spring back in the center. The syrup soak still works, just brush it on while the cakes are warm.
How do I know it is done without drying it out?
Look for a deep golden top and a tester that comes out with moist crumbs, not wet batter. Also, the cake should spring back lightly when you press the center.
My glaze soaked in. What happened?
The cake was likely still warm or the glaze was too thin. Let the cake cool fully before glazing, and add more powdered sugar if you want a thicker, set-on-top glaze.
Why did my cake sink in the middle?
Usually it is underbaking or overmixing. Loaf cakes need the center fully set, so rely on the toothpick test plus that spring-back feel. Also, once you add flour, mix just until you do not see dry streaks. Overmixing can make the middle rise fast and then collapse.