Step 1. Proof the yeast: stir the yeast into the warm milk and let sit 5–10 minutes until foamy.

Step 2. Make a shaggy dough: in a large bowl, whisk flour, sugar, salt, lemon zest (and vanilla if using). Add egg, softened butter, and the foamy milk. Stir with a spoon until no dry flour remains—the dough will look rough.

Step 3. Knead the dough (choose one):

• Stand mixer: knead with a dough hook on medium-low for 5–7 minutes.
• By hand: knead on a lightly floured counter 7–10 minutes (push–fold–turn rhythm).
  Texture cues: dough should be soft and slightly tacky but not sticking to your hands. If too sticky, dust in 1 tablespoon flour at a time; if stiff/dry, knead in 1–2 teaspoons milk. It’s ready when smooth and elastic and stretches thin without tearing (a loose “windowpane”).

Step 4. First rise: place dough in a lightly greased bowl, cover, and let rise 60–90 minutes in a warm spot until puffed (about 1½–2×). If unsure, do a finger-poke test—the dent should slowly spring back.

Step 5. Prep pan and plums: line or grease a cookie sheet. Wash, pit, and slice Italian plums into quarters/thin wedges. (Optional: toss fruit with 1–2 Tbsp sugar.)

Step 6. Shape the dough: turn dough onto the pan and pat it out evenly to about ½-inch thick. Press a tiny rim around the edge. Rest 10–15 minutes.
Juice guard (optional): lightly dust the half that will get plums with 1–2 teaspoons fine breadcrumbs or flour.

Step 7. Arrange toppings: on one half, lay plum wedges skin-side down in slightly overlapping rows; sprinkle 1–2 Tbsp sugar. On the kid-friendly half, sprinkle a light, even layer of sugar and cinnamon over the plain dough.

Step 8. Bake at 350°F (175°C) for 20–25 minutes; start checking at 18–20. It’s done when edges are golden, the plain side is lightly browned, and the plums look jammy. Tent loosely with foil if browning too fast before the center sets.

Step 9. Cool slightly, slice, and serve—the plum side for fruit lovers, the sugared plain side for picky eaters.