In a medium bowl, combine the softened cream cheese with 1/3 cup of granulated sugar. Beat until the mixture is fluffy and smooth. Add in the egg yolk and vanilla extract, mixing well until everything is combined. Set this aside to allow the flavors to meld.

In a small bowl, stir together 1/2 cup of flour, brown sugar, and ground cinnamon for the crumble topping. Cut in the cold butter until it resembles small crumbs. Pop this mixture into the refrigerator while you prep the bread.

Preheat your oven to 350°F (175°C) and grease a 9×5 inch loaf pan. In a medium bowl, whisk together the flour, baking soda, and salt.

In a large bowl, cream the softened butter with 1 1/2 cups of granulated sugar until it is light and fluffy. Beat in the eggs, one at a time, adding in the vanilla extract.

Gradually blend in the dry ingredients while alternating with the sour cream, creating a smooth batter. Gently fold in the fresh blueberries, taking care not to crush them.

Pour half of the batter into the prepared loaf pan. Next, dollop half of the cream cheese filling onto the batter. Use a knife to gently swirl the cream cheese into the batter for a marble effect.

Add the remaining batter on top, followed by the rest of the cream cheese mixture. Again, swirl slightly to combine. If desired, sprinkle the crumble topping over the top.

Place the loaf pan in the preheated oven and bake for 55-65 minutes or until a toothpick inserted into the center comes out clean. Keep an eye on the bread during baking, as ovens can vary in temperature.

Once baked, allow the bread to cool in the pan for 10-15 minutes before transferring it to a wire rack to cool completely. Slice and serve once cool, and enjoy the wonderful tastes and textures of your homemade Blueberry Cream Cheese Bread!