Milk should be cooled to about 100 degrees. Dissolve the yeast in the lukewarm water and add 1/4 c. of the cooled milk and 3 c. sifted flour. Cover the sponge with a cloth and let it ripen until bubbles appear on the surface and it is about to drop in the center. Pour the remaining milk over the sponge. Add the egg yolks, sugar and salt and beat until the ingredients are well blended. Add 1 cup flour and beat well. Blend in the butter. Add more flour gradually to make a smooth dough, or until 10 to 11 cups have been added. Some flours absorb more liquid than others. Knead in the sultanas, almonds, and citron, along with the lemon rind which should be mixed with the rum. Knead the dough until the fruits and nuts are dispersed well through it and it is smooth. Dust the top lightly with flour and let it rise in a warm place about 45 minutes. Punch it down and let stand for 20 minutes. Divide the dough in half and knead the pieces until smooth. Let them stand for 10 minutes longer. Place one ball of dough on a lightly floured board, and with a rolling pin, press down the center of the ball, and roll the pin to and fro 4 to 5 times, pressing all the time to make an elliptical shape 6 inches long and 3 1/2" wide. The center rolled part should be 1/8" thick and 4 inches long. Both ends should remain untouched, resembling rather thick lips. Place this rolled out piece of dough on a buttered baking sheet and brush the center part with melted butter. Fold one lip toward the other and on the top of it. Press the fingertips down near and below the lips, pulling somewhat apart. Give a pull away from each end, pointing them toward the lips. The shape should resemble a waning moon. Repeat the process with the second piece of dough. (Unless you have gone completely crazy by now! note: my comment, not Gourmet's). Let the Stollen rise, covered in a warm place until they double in bulk, about 1 1/2 hours. Bake them in a moderately hot oven (375 degrees) for 35 to 40 minutes. Do not overbake them. Cool them on racks. Brush them with butter and cover with vanilla sugar.
Source: Gourmet , Old Vienna Cookbook Gourmet Books, Inc., 1959 Barbara Day :::GWHP32A