Notes: Fresh yeast, sometimes called cake yeast, is the key to this dough, which rises overnight in the fridge. Because fresh yeast is already moistened and active, you don't have to dissolve it in warm water before using. You'll find paper-wrapped 0.6-ounce cubes of fresh yeast in the refrigerator case at the grocery store. This recipe calls for half a cube; wrap remainder in plastic wrap and chill for up to 1 week.
2 1/4 to 2 1/2 cups all-purpose flour
1/4 cup granulated sugar
1/2 teaspoon salt
1/2 cube fresh yeast (see notes)
2/3 cup milk
1/4 cup (1/8 lb.) butter, at room temperature, cut into chunks
2 ounces cream cheese, at room temperature, cut into chunks
1/2 cup berry jam
1 large egg yolk
How to Make It
In a food processor or a standing mixer fitted with the paddle attachment, whirl or mix 2 cups flour and the sugar, salt, yeast, and milk until a sticky dough forms.
Add butter and cream cheese and pulse or mix on low speed until just blended. Pulse or increase speed and beat until thoroughly incorporated, about 1 minute. Pulse or beat in 1/4 to 1/2 cup more flour as needed, 2 tablespoons at a time, until the dough begins to pull away from the sides of the bowl (dough will look sticky). If using food processor, scrape dough into a large bowl. Cover dough and chill at least 12 hours or up to 1 day.
Scrape dough onto a lightly floured surface. Divide in half. With a lightly floured rolling pin, roll each piece into an oval about 12 inches long and 6 inches wide. Spoon jam down center of each. Fold one long side of each oval over jam. Fold other side over, as if folding a letter. Place rolls about 3 inches apart on a buttered or cooking parchment-lined 12- by 15-inch baking sheet. Cover with plastic wrap; let stand 30 minutes.
In a small bowl, mix egg yolk and 2 tablespoons water. Brush rolls lightly with egg mixture.
Bake in a 350° regular or convection oven until golden brown, 20 to 25 minutes. With a wide spatula, transfer to a rack and cool completely. With a serrated knife, cut roll diagonally into 2-inch-wide slices. Sprinkle slices with powdered sugar.