Prepare Blueberry Filling by combining blueberries, sugar, and lemon juice in a saucepan over medium heat. Cook until thickened, then stir in cornstarch slurry and cook for an additional minute.

Make Dough: In a saucepan, warm milk and butter (100-110°F). Dissolve sugar and salt in this mixture, sprinkle yeast on top. After blooming for 5 minutes, add sourdough starter and mix in flour until smooth. Knead for 8-10 minutes until elastic.

First Rise: Place dough in an oiled bowl, cover, and let rise in a warm place for about 1 hour.

Prepare Filling: Melt butter in a bowl, combine brown sugar, cinnamon, and nutmeg. Prepare your dough for rolling once risen.

Roll Out Dough: Turn dough onto a floured surface, roll into a rectangle, brush with melted butter, sprinkle cinnamon mixture and cooled blueberries, leaving edges for sealing.

Shape Rolls: Roll the dough tightly into a log, slice into 12 pieces, and arrange in a greased baking dish.

Second Rise: Cover rolls and let rise for 1 hour until puffy.

Bake: Preheat oven to 350°F. Bake rolls for 30-35 minutes or until golden brown.

Make Frosting: Beat cream cheese and remaining butter, gradually add powdered sugar and reserved blueberry filling.

Frost and Serve: Cool rolls for 5 minutes, then frost generously while warm.