In a small bowl, mix the warm milk with a pinch of sugar and sprinkle the yeast on top. Let it sit for about 5-10 minutes, until it becomes frothy.

In a large bowl, whisk together the flour, sugar, and salt.

Add the yeast mixture, softened butter, eggs, vanilla, and lemon zest (if using) to the dry ingredients. Stir together until a rough dough forms.

Transfer the dough to a floured surface and knead for 10-12 minutes, until the dough becomes smooth and elastic.

Place the dough in a greased bowl, cover with a damp cloth, and let it rise in a warm spot for 1-1.5 hours, or until it has doubled in size.

Mix the raspberry jam with cornstarch and water in a small saucepan. Heat over medium-low until the mixture thickens slightly, then set aside to cool.

Once the dough has risen, punch it down and roll it out into a rectangle (about 10×15 inches).

Spread the cooled raspberry filling evenly over the dough, leaving a ½-inch border around the edges.

Starting from the long side, roll the dough into a tight log. Slice the log in half lengthwise to expose the jam-filled layers, then carefully twist the two halves together, keeping the cut sides up.

Transfer the twisted dough into a greased 9×5-inch loaf pan. Cover with a towel and let it rise again for 30-40 minutes.

While the dough is rising, preheat your oven to 350°F (175°C).

Brush the top of the loaf with melted butter, then bake for 35-40 minutes until golden brown.

Let the bread cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

In a small bowl, whisk together the powdered sugar, lemon juice, and milk. Drizzle the glaze over the cooled loaf for a tangy-sweet finish.