1-ACTIVATE THE YEAST: ACTIVATE THE YEAST: In a small bowl, combine warm milk and a pinch of sugar, then sprinkle the yeast over the top. Let it sit for 5-10 minutes until foamy.
2-MIX DRY INGREDIENTS: MIX DRY INGREDIENTS: In a large mixing bowl, whisk together the flour, granulated sugar, and salt until evenly combined.
3-COMBINE WET INGREDIENTS: COMBINE WET INGREDIENTS: Add the foamy yeast mixture, softened butter, eggs, vanilla extract, and lemon zest (if using) to the dry ingredients. Mix until a shaggy dough forms.
4-KNEAD THE DOUGH: KNEAD THE DOUGH: Transfer the dough to a lightly floured surface and knead by hand for 10-12 minutes, until the dough becomes smooth and elastic. Add small amounts of flour if the dough is too sticky.
5-LET DOUGH RISE: LET DOUGH RISE: Place the kneaded dough in a lightly greased bowl. Cover with a damp towel and let rise in a warm area for 1 to 1 ½ hours, or until doubled in size.
6-THICKEN THE FILLING: THICKEN THE FILLING: While the dough rises, stir together raspberry preserves, cornstarch, and water in a small saucepan. Cook over medium-low heat, stirring constantly, until the mixture thickens slightly. Set aside to cool completely.
7-ROLL OUT THE DOUGH: ROLL OUT THE DOUGH: After the first rise, punch down the dough and roll it into a 10×15-inch rectangle on a floured surface.
8-ADD THE FILLING: ADD THE FILLING: Spread the cooled raspberry mixture evenly over the dough, leaving a ½-inch border on all sides.
9-FORM THE LOAF: FORM THE LOAF: Starting from one long edge, roll the dough into a tight log. Slice the log lengthwise down the center to reveal the layers, then twist the two halves together with the cut sides facing up.
10-SECOND RISE: SECOND RISE: Gently transfer the twisted dough into a greased 9×5-inch loaf pan. Cover and let rise for another 30-40 minutes.
11-PREHEAT THE OVEN: PREHEAT THE OVEN: While the loaf is rising, preheat your oven to 350°F (175°C).
12-BAKE THE LOAF: BAKE THE LOAF: Brush the top of the loaf with melted butter. Bake for 35-40 minutes until golden brown and fully baked. If it browns too quickly, cover loosely with foil for the final 10 minutes.
13-COOL THE LOAF: COOL THE LOAF: Let the baked loaf cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before glazing.
14-MAKE THE GLAZE (OPTIONAL): MAKE THE GLAZE (OPTIONAL): In a small bowl, whisk together powdered sugar, lemon juice, and milk until smooth. Drizzle over the cooled loaf.