Place the water, butter, sugar and yeast in the bowl of a mixer. Stir until the yeast dissolves. Add the flour, salt, and wheat germ, if using. Stir with a wooden spoon until the flour is moistened. Then put the bowl on the mixer stand with the dough hook. Knead the mixture on low speed until it comes together. Then knead it on medium speed until the soft dough is smooth and comes away from the sides of the mixing bowl, about 5 to 6 minutes. Place dough in a large ungreased bowl, covered with plastic wrap. Allow the dough to rise at room temperature for 2 to 3 hours. It will have almost doubled in volume. While the dough rises, make the filling. Combine the Love'n Bake™ Poppy Seed Filling with the egg and vanilla stirring until it is well blended. Grease a 9-inch x 4-inch loaf pan. Scrape dough onto a lightly floured work surface. Divide the dough into three equal pieces. Roll each piece of dough into a rope about 9 inches long. Flatten each piece of dough. Spread one third of the filling over each piece of dough keeping the edges plain. Fold over each piece of dough to cover the filling. Pinch the edges to seal each rope of dough. Braid the three filled ropes of dough. Tuck the ends under to make a neat loaf then transfer the dough to the prepared pan. Cover the dough loosely with plastic and let it rise until the dough increases by half its size, for about 30 to 45 minutes. It should feel soft but still spring back slightly when poked with your finger. One hour before baking, put the oven rack on the second shelf from the bottom of the oven and place the baking stone on the rack. Place a small pan for water on the floor or lower shelf of the oven. Preheat the oven to 475 °F. Just before baking, brush the dough with the egg wash and sprinkle it with the poppy seeds. Place the pan on the baking stone. Carefully pour about 1 cup of warm water into the pan on the oven floor. Reduce the heat to 425°F. Bake the loaf for 40 to 50 minutes until the crust is golden brown. (Thirty minutes into the baking, you may remove the loaf from the pan to finish baking directly on the stone.) Tap the bottom of the loaf; a hollow sound means its done. Remove the bread from the oven and immediately place it on a wire rack to cool completely before storing. * If bread flour is unavailable, all-purpose flour may be used. Reduce the water to 1 1/2 cups.