In a large bowl (the bowl of a stand mixer if you have one) sprinkle the yeast over the warm milk, along with a pinch of sugar. Let stand 5 minutes, then whisk to dissolve the yeast. Add 3/4 cup of the flour and stir well to make a thin, sticky dough. Cover with plastic wrap and let stand in a warm place until bubbly and doubled in volume, about 20 minutes.
Add the remaining flour (up to 2 1/2 cups) along with the butter, sugar, vanilla, almond extract, lemon and orange zest and salt. Attach the dough hook, if you're using a stand mixer, and beat on medium-low speed or stir by hand until the dough comes together. Continue beating or kneading until the dough is smooth and elastic, adding more flour if needed. Add the dried fruit and nuts and mix until they are incorporated into the dough. Cover the bowl with a tea towel or plastic wrap and let stand in a warm place until the dough has doubled in volume, about 1 1/2 hours.
Turn the dough out onto a lightly floured work surface and cut in half. Very gently shape each portion into a ball—do not knead the dough, as you want to retain its light texture. Place the balls on the floured work surface and cover each with a clean kitchen towel. Let stand in a warm place until the dough looks puffy but not doubled, about 45 minutes.
On a parchment-lined sheet, press each piece of dough into a thick round about 7 or 8 inches in diameter. Fold about a third of the dough over itself, as if you were starting to fold a letter; press a ridge in the bottom dough with your fingers at the edge of the folded over part; this will keep the stollen layers from separating when baked. Cover with a tea towel and let stand in a warm place until the dough looks puffy but not doubled, about 30 minutes. Preheat the oven to 325°F. Uncover the loaves and bake for 30 minutes, until deep golden.
Shower with a generous amount of icing sugar while still warm. (If you like, brush warm loaves with melted butter first.)