In a large mixing bowl, combine warm milk, active dry yeast, and granulated sugar. Let sit for 5-10 minutes until frothy. Gradually mix in flour, salt, melted butter, beaten eggs, vanilla extract, and optional lemon zest, kneading for 10-12 minutes until smooth.

Place kneaded dough in a greased bowl, cover, and let rise in a warm place for 1 to 1.5 hours, or until doubled in size.

Mix raspberry preserves with cornstarch and water in a saucepan. Heat over medium-low until thickened (3-5 minutes), then allow to cool.

Punch down the risen dough, roll onto a floured surface into a rectangle. Spread cooled raspberry filling over the surface, roll into a log, slice in half, and twist to create a braid.

Place the braided loaf into a greased loaf pan, cover, and let it rise for 30-45 minutes until puffy.

Preheat oven to 350°F. Brush loaf with melted butter, bake for 35-40 minutes, covering loosely with foil after 30 minutes.

Allow to cool for 10 minutes in the pan, transfer to a wire rack. Whisk together powdered sugar, lemon juice, and a splash of milk for glaze, drizzle over the cooled loaf.