You may substitute regular plums in this recipe, but the smaller Italian prune plums are sweeter. This is a great cake to make for breakfast, because the dough rises overnight in the refrigerator.
For dough: In a bowl, whisk together lukewarm water and yeast; set aside.
In the bowl of a stand mixer or food processor fitted with a dough blade, add flour, sugar, salt, butter, and egg. Add yeast mixture and pulse until a ball forms. It should be sticky; add more water, a tablespoon at a time, if needed. Remove dough from processor and transfer to a lightly oiled bowl. Cover with plastic wrap and refrigerate overnight. It will rise only slightly.
When dough is ready, adjust oven rack to middle position and preheat to 400°F. Grease a 9-inch springform pan.
Remove dough from refrigerator and set aside. Halve plums (if using regular plums, cut into quarters) and remove pits; set aside.
For topping: In a bowl, combine brown sugar, flour, salt, and butter. Rub mixture with your fingers until crumbly; then stir in almonds and set aside.
Remove dough from plastic wrap and, on a lightly floured work surface, press with your fingers into a 9-inch circle. Place dough in prepared pan. Leaving a ½-inch border around edge of dough, arrange plums snugly, like fallen dominoes, in circles over surface of dough.
Sprinkle topping on plums. Bake for 40 to 45 minutes, or until topping and crust are light brown.