Starter: In a small bowl, dissolve the yeast in warm milk. Add sugar and flour, mix well, cover with a towel, and let it sit in a warm place for about 15 minutes until bubbly.
Dough: In a large bowl, beat the egg yolks, whole eggs, sugar, and vanilla sugar until light and fluffy. Stir in the cream, salt, and lemon zest (if using). Mix until smooth.
Add the risen starter to the egg mixture and mix well. Gradually add the flour, kneading as you go. The dough should be soft and slightly sticky.
Knead the softened butter into the dough a little at a time. Once fully incorporated, cover the bowl with plastic wrap or a clean towel and let rise in a warm place for 2 hours, or until doubled in size.
Punch down the dough (lightly oil your hands if needed). Gently knead in the raisins and candied fruit.
Divide the dough into 3 parts and shape each part into a ball.
Place into greased paper molds or baking pans. Cover loosely and let rise for another 30–60 minutes, until the dough reaches the top of the molds.
Preheat the oven to 180°C / 356°F. Bake the breads for 35–40 minutes, or until golden brown and a skewer inserted into the center comes out clean. If the tops brown too quickly, tent them with foil.
Let the breads cool, then decorate with glaze.
Glaze: Combine the egg white and sugar in a heatproof bowl and place over a pot of simmering water (double boiler).
Stir constantly until the sugar fully dissolves (don’t let the bowl touch the water).
Remove from heat and beat with a hand mixer until stiff peaks form. Add lemon juice while mixing to stabilize the glaze.
Spread over the cooled bread and decorate as desired (sprinkles, nuts, dried fruit, etc.).