For the dough:
1/2 cup (1 stick) unsalted butter
1/2 cup sugar
1 teaspoon salt
2 teaspoons active dry yeast
1/2 cup warm water
1 cup sour cream
2 large eggs, beaten
4 cups all-purpose flour
For the filling:
1 pound cream cheese
3/4 cup sugar
1 large egg
1/8 teaspoon salt
2 teaspoons vanilla extract
For the glaze:
1 cup powdered sugar
2 tablespoons milk
1/2 teaspoon vanilla extract
Melt the butter in a saucepan over low heat or in the microwave in 30-second intervals. Stir in the sugar and salt to form a thick paste and partially dissolve the sugar.
In the bowl of a standing mixer, sprinkle yeast over the warm water. Stir until dissolved. Add the butter-sugar mixture, sour cream, eggs, and flour. Stir a few times with a spatula to form a shaggy dough, then knead with a dough hook on medium-low speed for 5 to 7 minutes, until the dough smooths out and all the flour is incorporated. This won't be quite the consistency of bread dough; it will be more like a thick batter.
Cover the mixing bowl and refrigerate overnight or for up to 24 hours. In the morning, the dough won't be quite doubled, but it should look puffed and risen.
When ready to bake the loaves, remove the cream cheese for the filling from the refrigerator and let it warm on the counter for about 30 minutes. Line 2 baking sheets with parchment or nonstick baking mats.
Sprinkle a work surface liberally with flour. Transfer the dough on top, then clean and dry the mixing bowl. To make the filling, combine the softened cream cheese, sugar, egg, salt, and vanilla extract in the bowl of the cleaned mixer and beat until creamy and combined, scraping down the bowl once or twice.
Divide the dough into 6 equal pieces with a pastry scraper or a sharp knife and move them to side of your work surface. Working with one piece of dough at a time, pat the dough into a rough rectangle and sprinkle liberally with flour. Use a rolling pin to roll the dough to a rectangle roughly 12 inches long by 8 inches tall and 1/8 to 1/4 inch thick. The dough is easy to roll out, but can be fairly sticky so use extra flour as needed.
Scoop 1/3 cup of the filling mixture and spread it over the dough in a thin layer, leaving a 1-inch border clear on the tops and sides. Carefully roll up the dough starting at the long side on the bottom. If the dough sticks to your work surface, use your pastry scraper or knife to gently scoop it up. Once rolled, transfer the roll to the baking sheet, seam-side down, and tuck the ends underneath. The finished roll will be 9 to 10 inches long.
Continue rolling out each piece