In a medium saucepan, combine fresh blueberries, ¾ cup sugar, and 1 tablespoon lemon juice. Over medium heat, bring the mixture to a boil, stirring occasionally. Once boiling, reduce the heat and let it simmer for about 15 minutes until it thickens. Remove from heat and refrigerate until needed.

In a mixing bowl, beat together 8 oz of cream cheese and ½ cup sugar using an electric mixer until smooth and creamy. Set aside to reach room temperature.

Warm 1 cup of milk to 100-110°F. In a separate bowl, combine 1 teaspoon sugar and the active dry yeast, then stir in the warm milk. Let it sit for about 5 minutes until foamy. Mix 4 cups flour, ⅓ cup sugar, and 1 teaspoon kosher salt. Add in the yeast mixture, 2 eggs, and 1 teaspoon vanilla extract, and beat until smooth.

Gradually mix in 10 tablespoons of very soft unsalted butter into the wet dough. Use the mixer on low speed to ensure the butter is evenly incorporated.

Transfer the dough into a greased bowl, covering it. Allow it to rise in a warm place for 1 to 1½ hours until doubled.

Punch down the risen dough and divide into two portions. Roll each into a rectangle about 12x18 inches. Spread half of the cream cheese filling and half of the blueberry preserves over each rectangle, then roll each tightly into a log.

Cut each log lengthwise in half and twist the two halves together in a spiral shape, placing each twisted log into greased loaf pans.

Cover the loaf pans and let the babka rise for about 1 hour, until puffed and nearly doubled.

Preheat your oven to 350°F. Bake the risen babka for 40 minutes until golden brown and a skewer comes out clean.

Prepare a sugar syrup by combining ⅓ cup sugar and ⅓ cup water in a small saucepan over medium heat until dissolved. Brush this syrup over the hot babka. Cool in the pan for about 10 minutes before transferring to a wire rack.