In a small bowl, dissolve the yeast and 1 teaspoon of the dough's granulated sugar in warm water and warm milk. Let sit for about 5 to 10 minutes until foamy.

In a large mixing bowl or the bowl of a stand mixer, combine 480 ml of the flour, the remaining sugar, and the salt. Add the yeast mixture, melted butter, eggs, and vanilla extract. Beat on medium speed until smooth.

Gradually add the remaining flour (about 180 ml) and switch to a dough hook. Knead on medium-low speed for about 5 to 7 minutes, or by hand on a lightly floured surface, until the dough is smooth and slightly tacky but not sticky.

Place the kneaded dough in a greased bowl, turning once to grease the top. Cover with a damp cloth or plastic wrap and let rise in a warm, draft-free place for about 60 minutes, or until doubled in size.

In a small bowl, rub the lemon zest into the filling's granulated sugar with your fingertips until fragrant and pale yellow. Grease a 9x5-inch loaf pan and set aside.

Punch down the dough and turn it out onto a lightly floured surface. Roll the dough into a large rectangle, approximately 12x20 inches. Spread the softened butter evenly across the surface, then sprinkle the lemon sugar and fresh blueberries uniformly on top.

Cut the rectangle crosswise into 5 equal strips. Stack the strips on top of each other, then cut the stack into 6 equal squares. Arrange these squares cut-side up (like pages in a book) in the prepared loaf pan.

Cover the loaf pan loosely and let the dough rise a second time for about 30 to 45 minutes, until puffy and filling the pan. Preheat your oven to 177 °C (175 °C) during the last 15 minutes of rising.

Bake the bread in the preheated oven for 30 to 35 minutes, until the top is deeply golden brown and the center is baked through. If the top browns too quickly, tent it loosely with aluminum foil.

While the bread cools slightly in the pan, whisk together the powdered sugar and lemon juice to create a smooth, pourable glaze. Drizzle the glaze generously over the warm bread before serving.