1. To make dough, combine flours, salt and all but 1 tablespoon sugar in mixer fitted with dough attachment and mix on medium speed. In a small bowl, stir yeast with one tablespoon warm water and reserved tablespoon sugar just until sugar and yeast have dissolved. Reduce mixer speed to low, add yeast mixture, milk, eggs and vanilla. Beat until dough is shiny and elastic, 10 to 15 minutes.
2. Add one stick butter by spoonfuls until thoroughly incorporated, then beat on low speed for about 5 minutes. When finished, dough should be silken and rich like very thick ice cream. Transfer to a large bowl, cover with plastic wrap and set aside. When dough has doubled in size, after 2 hours, flour a cutting board and your hands. Then push dough down on board, cover well with plastic wrap and refrigerate for 1 to 2 hours or overnight.
3. To make filling, pur?e apricot preserves in a food processor until smooth. In a small bowl, combine cake crumbs, preserves and butter; mix until smooth. Set aside. Grate chocolate by hand in large holes of a box grater or in a food processor. If using a food processor, pulse into large chunks. Set aside.
4. To make streusel topping, in a small bowl mix flour, sugar and cinnamon. Add cold butter and using your fingers, mix together until crumbly. Set aside.
5. To assemble, line one Bundt pan or two 8 1/2 by 4 1/2-inch loaf pans with parchment paper, not letting paper come more than 1 inch above top of pans. Remove dough from refrigerator and divide it in half. On a lightly floured surface, roll one piece of dough into a 12 x 8-inch rectangle.
6. Using a metal spatula, spread half the apricot filling over dough within 1/2 inch of edges. Sprinkle with half the grated chocolate. Beginning with long side, roll dough up tightly and fold in ends. Twist babka lengthwise to create a spiral, holding one end of babka in each hand. Place twisted babka in half the prepared Bundt pan or in a loaf pan, pressing dough firmly into pan. Melt remaining 2 tablespoons butter. Brush babka top with melted butter and sprinkle with half the streusel. Repeat with second half of babka dough. Cover loosely with plastic wrap. Let loaves rise at room temperature until they reach top of pan or about doubled in volume, about 2 hours.
7. Heat oven to 350 degrees and bake for about 45 minutes, or until a cake tester inserted in center comes out clean. Allow babka to cool for 30 minutes before cutting. Slice babka and serve.
Yield: 1 large Bundt babka or 2 loaf babkas.
Note: Chocolate almond paste filling with rum-soaked raisins (From Mrs. London?s) or cinnamon-raisin filling (from Katja Goldman) may be substituted in Step 6.
For Cinnamon Raisin Filling:
1. In a small bowl, stir sugar and cinnamon together. Place raisins in another bowl and plump with 1/2 cup just- boiled water for a few minutes, and drain.
2. Sprinkle half the cinnamon-sugar mixture on one piece of rolled out dough and then half the raisins. Repeat with remaining dough.
Note: If using this filling, add up to 1 tablespoon cinnamon to streusel topping
For Chocolate Almond Paste Filling :
1. Place almond paste, egg white and melted butter in a food processor. Pulse until mixed. Add sponge cake crumbs and pulse again. Add enough water, about 4 tablespoons, to make filling spreadable. Set aside.
2. In a small bowl, plump raisins in a little just-boiled water for a few minutes, then drain. Add rum, stir and let sit for at least a half hour. Set aside. In another small bowl, stir sugar and cinnamon together.
3. On one piece of rolled out dough, spread half the almond paste filling then half the chocolate. Sprinkle with half the raisins and half the cinnamon-sugar. Repeat with the second piece.
Yield: Filling for one Bundt babka or two loaf babkas