Warm a small portion of the milk until lukewarm, then dissolve the fresh baker's yeast in it.

Add both flours, the remaining milk, sugar, and vanilla seeds to the stand mixer bowl.

Mix the dough briefly, then add the egg and lightly beaten egg yolks.

Add melted unsalted butter and salt, then knead until the dough is elastic and well developed, about 6 minutes.

Shape the dough into a ball, then place it in a lightly oiled bowl.

Cover the bowl and let the dough rise in a warm place until nearly doubled.

Combine softened butter, sugar, and ground cinnamon until smooth.

Lightly flour the work surface, then roll the risen dough into the thinnest possible rectangle.

Spread the cinnamon butter evenly over the dough, then scatter the lemon zest over the filling.

Roll the dough rectangle tightly from the long side, then cut it lengthwise while leaving one end attached.

Twist each cut section into a spiral, then stack the two spirals in a nonstick springform panettone mold.

Let the shaped dough rise until doubled in size, then preheat the oven to 175°C.

Bake at 175°C for 30 minutes, then cover the top with aluminum foil.

Lower the oven to 165°C and bake for 20 more minutes, then cool before slicing.