Soak 1 tbsp of crystallized sugar and yeast in lukewarm milk for 3 minutes. Mix and let rest in a warm place, away from drafts (e.g., a warm, turned-off oven) until the mixture has doubled in volume – about 5 minutes. Pour the yeast mixture into a bowl, add the egg yolks, vanilla, lemon zest, salt, and remaining sugar. By hand, gradually incorporate 500 ml of flour until a homogeneous consistency is achieved – the dough should be able to be shaped into a ball. Then, incorporate the small pieces of butter and beat until the dough becomes more consistent and elastic. Add 125 to 250 ml of flour, or until the dough is firm and oily, but not sticky. Place the ball on a lightly floured surface. Knead the dough for about 10 minutes. When the dough has become smooth and shiny, place it in a buttered bowl, sprinkle lightly with flour, cover with a dish towel, and let it rest in a draft-free place for about 45 minutes, or until it has doubled in volume. With a firm punch, flatten the dough in the bowl. Add the candied lemon and raisins and knead until the fruit is evenly distributed, with as little manipulation as possible. Line a large bread mold with brown paper, buttering it well on both sides, pour in the dough, draw a cross on top, cover with buttered paper, and let it rise again in a warm place for 15 minutes. Remove the paper from the top and brush with softened butter using a brush. Preheat the oven to 400°F. Place the mold on the center rack and bake for 10 minutes. Reduce the oven temperature to 325°F and continue baking for 30 to 40 minutes, brushing again with melted butter. The cake is cooked when the surface is golden and crunchy. Remove the cake from the oven, remove the paper, and let cool for 15 minutes before unmolding.