With a mixer, beat 1 cup of room-temperature unsalted butter, 170g of room-temperature cream cheese, ⅓ cup of sour cream, and ½ teaspoon of salt until smooth. Mix in 2 cups of all-purpose flour until the dough comes together.
Divide into 3 pieces and flatten each into a disk. Wrap and refrigerate for about 1 hour, until firm but not rock hard.
For the filling, pulse ½ cup of packed brown sugar, 1 cup of chopped walnuts, ½ cup of raisins, and 1 tablespoon of ground cinnamon in a food processor until finely chopped.
Roll each disk into a 10in / 25cm circle, brush with water, and spread a third of the filling to the edges. Cut into 12 wedges and roll each one up from the wide end.
Place on parchment-lined baking sheets, brush with milk, and sprinkle with sugar. Chill while you preheat the oven to 350°F / 175°C.
Bake for 25-30 minutes, until golden brown. Cool on a wire rack.
