In a large bowl, combine the flour, sugar, instant yeast, and salt.

In a separate bowl, mix the warm milk, softened butter, and eggs until well combined.

Slowly pour the wet mixture into the dry ingredients and mix until a dough forms.

Knead for about 10 minutes until smooth and elastic.

Place the dough in a lightly greased bowl, cover it with a clean kitchen towel, and let it rise in a warm place for about 1 hour, or until doubled in size.

In a small bowl, mix together the blueberries, lemon zest, and sugar.

Once the dough has risen, punch it down and roll it out into a rectangle shape.

Brush the melted butter over the dough, then sprinkle the blueberry mixture evenly on top.

Roll the dough tightly into a log, then slice it in half lengthwise.

Twist the two halves together to form a braid and place it in a greased loaf pan.

Cover the braided loaf with a kitchen towel and let it rise again for about 30-45 minutes.

Preheat the oven to 350°F (175°C) and bake the babka for 30-35 minutes, or until golden brown.

While the babka cools, whisk together the powdered sugar and lemon juice until smooth, and drizzle it over the cooled loaf.