Ukrainian coffee cake

1 tsp sugar
1/4 cup lukewarm water
1 pkg dry granular yeast
3/4 cup scalded milk, lukewarm
1/2 cup flour
2 whole eggs
3 egg yolks
1/2 tsp salt
1/2 cup sugar
1/4 cup melted butter
1 tsp vanilla
2 to 2-1/2 cups sifted flour
Filling:
1/2 cup chopped nuts
1/2 cup brown sugar
1 tsp vanilla

1. Dissolve the sugar in the lukewarm water, sprinkle the yeast over it, and let it stand until softened. Combine with the lukewarm milk and 1/2 cup of flour. Beat well, cover, and let the sponge rise in a warm place until light and bubbly. Beat the whole eggs and the egg yolks together along with the salt. Add the sugar gradually and continue beating. Beat in the butter and vanilla. Combine with the sponge, add the flour, and knead in the bowl for about 10 minutes, or beat vigorously with a spoon. This dough is very soft.
2. Cover and let it rise until double in bulk. Punch down and let it rise again. Butter a very large tube pan and sprinkle it with fine bread crumbs. Spoon one-half of the dough into the pan. Mix the nuts, sugar, and vanilla. Sprinkle one-half of this mixture over the dough. Cover with the remaining dough and top with the rest of the nut mixture. Let it rise in a warm place until it is more than double in bulk.
3. Bake in a moderate oven (375 F) for 10 minutes, then lower the temperature to 325 F and bake for 35 to 40 minutes longer. If necessary, cover the top with aluminum foil. Allow the cake to stand in the pan for 10 minutes to cool slightly. Remove it from the pan very gently.