Polenta Budino With Plum Marmellata

Bring 2 cups water to a boil in a medium saucepan. Whisking constantly, gradually add polenta; whisk until smooth. Reduce heat to low and cook polenta, whisking and breaking up any lumps, until thickened, about 3 minutes. Whisk in granulated sugar, brown sugar, and salt (mixture will loosen) and cook, whisking often, until mixture thickens again and polenta is tender, 20 –25 minutes. Remove from heat and whisk in butter. Whisk egg yolk and cream in a small bowl to combine, then vigorously whisk into polenta. Transfer mixture to a large bowl and cover with plastic wrap, pressing directly onto surface. Let cool.