In a small bowl, dissolve the yeast in warm milk and let it sit for about 5 minutes until it becomes frothy.

In a large mixing bowl, combine the flour, sugar, salt, and lemon zest (if using). Make a well in the center and pour in the melted butter, yeast mixture, eggs, and vanilla extract. Mix everything together until a sticky dough forms.

Place the dough onto a lightly floured surface and knead for about 10-15 minutes until the dough becomes smooth and elastic. If the dough is too sticky, gradually add more flour as needed.

Place the dough in a greased bowl, cover it with a clean kitchen towel, and let it rise in a warm place for about 1-2 hours until it doubles in size.

Once the dough has risen, punch it down to release any air bubbles. At this point, you can add the chopped nuts or raisins (if desired) and knead them into the dough.

Divide the dough into two equal parts. Roll out each portion into a rectangular shape, about 1/2 inch thick.

Starting from one of the longer edges, tightly roll up the dough like a jelly roll. Place the rolled dough into greased loaf pans.

Cover the pans with a towel and let the dough rise for another 30-60 minutes until it doubles in size.

Preheat the oven to 350°F (175°C). Once the dough has risen, bake the cozonac in the preheated oven for about 30-40 minutes until golden brown on top and cooked through. You can also test for doneness by inserting a toothpick into the center of the bread; if it comes out clean, it's ready.

Remove the cozonac from the oven and let it cool in the pans for a few minutes. Then, transfer the bread to a wire rack to cool completely before slicing and serving.