In a small bowl, dissolve the yeast in warm water with a pinch of sugar. Let it sit for about 5-10 minutes until frothy.
In a large mixing bowl, combine the flour, sugar, and salt.
Make a well in the center and add the melted butter, eggs, warm milk, vanilla extract, and the yeast mixture.
Mix until a dough forms, then knead on a floured surface for about 10 minutes until the dough is smooth and elastic.
Place the dough in a lightly oiled bowl, cover with a clean cloth, and let it rise in a warm place for about 1-1.5 hours, or until it doubles in size.
In a large bowl, combine the ground walnuts, brown sugar, honey, melted butter, warm milk, cinnamon, and vanilla extract.
Mix until well combined. If using, stir in the raisins and lemon zest.
Punch down the risen dough and turn it out onto a floured surface.
Roll the dough into a large rectangle, about 1/4 inch thick.
Spread the walnut filling evenly over the rolled-out dough, leaving a small border around the edges.
Starting from one of the long edges, roll the dough tightly into a log.
Pinch the seams to seal and tuck the ends under to secure.
Place the rolled dough in a greased and floured bundt pan or loaf pan, seam side down.
Cover with a clean cloth and let it rise in a warm place for another 30-45 minutes.
Preheat your oven to 350°F (175°C).
Bake the potica for about 45-50 minutes, or until it is golden brown and sounds hollow when tapped.
If the top starts to brown too quickly, cover it loosely with aluminum foil.
Let the potica cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.
Slice and serve. Optionally, dust with powdered sugar before serving.
Enjoy your meal!