Whisk warm water, sourdough starter, and sugar in a large bowl until dissolved.
Add bread flour, salt, melted butter, egg, lemon zest, and lemon juice; stir until a shaggy dough forms.
Knead dough on a clean surface about 10 minutes until smooth and elastic.
Place dough in a lightly oiled bowl, cover, and let rise in a warm place for 4–5 hours until doubled.
Beat cream cheese until smooth in a mixing bowl; add sugar, egg, and vanilla extract and mix until creamy.
Refrigerate cream cheese filling while dough rises.
Punch down risen dough to release air and divide into two equal parts.
Roll each dough portion into a 1/4 inch thick rectangle.
Spread cream cheese filling evenly on one rectangle, leaving a 1-inch border.
Sprinkle blueberries over the cream cheese layer.
Fold second dough rectangle over the filling and seal the edges by pinching.
Shape dough into a round or oval loaf and place on parchment-lined baking sheet.
Mix lemon juice and honey; brush this wash over the top of the dough.
Preheat oven to 375°F (190°C) and bake bread for 35–40 minutes until golden brown and hollow sounding when tapped.
Remove bread from oven and cool on a wire rack for at least 15 minutes before slicing.