In a large bowl, combine yogurt, butter, eggs, sugar, salt, vanilla and yeast mixture. Add flour 1 cup at a time, until the dough comes away cleanly from the sides of the bowl. Turn dough out onto a lightly floured surface and, adding only enough flour to keep the dough from sticking to your hands or the work surface, knead dough about 5 minutes, until soft and pliable but not too sticky. Let dough rest while you clean and grease the bowl with a little bit of oil. Finish kneading dough until it's smooth and supple.

Place the dough in the greased bowl, turn the dough to coat all surfaces with the oil. Cover with plastic wrap and a clean towel, and let sit in a warm place about 1 1/2 hours, or until doubled.

Gently deflate the dough and divide it in half. Cover with plastic wrap and let rest on a lightly floured surface for 15 minutes. Form dough into desired shapes (see below). Cover with plastic wrap and let rise about 45 minutes. Preheat oven to 375 degrees. Brush loaves with egg wash and bake until golden brown, about 30-40 minutes, to an internal temperature of 190 degrees F. Remove the bread from the oven and let it cool on a rack.

Almond-Filled Braid: Working with half the Basic Sweet Dough at a time, roll dough into a 19-by-15-inch rectangle. Press two light lines on each rectangle, lengthwise, to divide dough into three equal sections. Spread purchased almond filling (American Almond Baker's Style Almond Schmear Filling is recommended) down center section, leaving 1 inch of clear space at either end and along the inside edges. Cut 1-inch wide strips from edge of filling to outer edge of the dough. Fold the ends over the filling. Bring the dough strips across the filing on a diagonal, alternating from side to side. Repeat with remaining piece of dough.

Cover loaves with plastic wrap and a clean towel, and let rise in a warm place until doubled in bulk, about 35 to 45 minutes. Preheat oven to 375 degrees. Brush tops of loaves with egg wash. Bake 25-35 minutes, or until loaves are a rich, golden brown. Cool loaves on racks. If desired, drizzle loaves with sugar icing (see directions below) and top with sliced almonds. Makes two braids. Other fillings can be used, such as strawberry jam with cream cheese.

Sugar Icing: Combine 1 cup (4 ounces) powdered sugar, 3 tablespoons heavy cream or 2 tablespoons milk, and a few drops of flavored extract such as lemon or orange.