Dissolve the yeast in a bowl with water. Allow it to sit for 5 minutes. Combine the sugar, eggs, vanilla, lemon zest, lemon juice, salt, butter, and yeast in a large bowl; beat together to combine.
Add in the flour in 2 or 3 batches, stirring to combine. Transfer the dough to a floured surface. Knead the dough until soft, adding more flour if necessary. Place the dough in a greased bowl and cover with a cloth. Allow it to rest and rise for 30 to 45 minutes. It should double in volume.
Turn the dough out again onto a floured surface, punch it down, and knead in the currants and raisins. Shape the dough into a ball and place in a buttered pan (about 2-quart size will work). Allow to rise again until doubled in volume, about 30 to 45 minutes.
Preheat the oven to 400 degrees F, bake the bread for 15 minutes. Then, reduce the heat to 350 degrees F, and bake for an additional 30 to 40 minutes.