In a heavy saucepan, bring 3 cups milk to a boil with half ½ cup granulated sugar and the ¼ teaspoon salt, watching so the milk does not scorch.
Reduce the heat to its lowest setting, add 1 ⅓ cups white rice, cover, and cook until soft (follow your rice's package time). Let it cool until no longer hot.
Prepare the pan and oven
Preheat the oven to 350°F (175°C). Grease the pan with ½ Tablespoon butter and dust with ½ Tablespoon breadcrumbs, or line it with parchment paper.
Make the custard
Cream 1 stick unsalted butter with the remaining sugar until pale and fluffy. Stir in 5 egg yolks and 1 Tablespoon lemon zest.
Fold the custard into the cooled rice. Whip 3 egg whites until softly peaked, then fold in gently.
Layer and bake
Spread half the rice mixture in the pan. Cover with 12 ounces canned plums, spread the rest of the rice on top, and smooth it. Bake for 40 minutes.
Snow top (optional)
Whip the reserved 2 egg whites to stiff peaks, then beat in the sugar a little at a time until glossy and firm.
About 10 minutes before the pudding is done, spread the snow over it and return it to the oven to finish, until golden.
Notes
The butter must be softened to room temperature so it creams properly.
Cool the rice before mixing it with the yolks, or the yolks may scramble.
You need 5 eggs in total: all 5 yolks go into the custard, 3 whites are folded into the rice, and 2 whites are reserved for the snow top.
The meringue top (sníh) is optional; skip it for an everyday version.
Serves 6 as a sweet main dish, or closer to 8 in smaller dessert portions.
Serve warm (soft) or slightly cooled (holds its shape better).
Store in the refrigerator up to 4 days. Best fresh; not suited to freezing.
Oven temperatures are for a conventional (non-fan) oven; for convection, lower by 25°F