In a large bowl, combine sugar, salt, yeast, 1 1/2 cups white flour and 1 cup oat flour. In 1 quart saucepan over low heat, heat milk and butter until very warm (120 - 130°F). Butter need not melt completely.
With mixer at low speed, gradually beat liquid into dry ingredients just until blended. Increase speed to medium and beat 2 minutes, occasionally scraping the bowl with a rubber spatula.
Reserve 1 egg white for brushing top of loaves. Gradually add egg yolk and remaining 2 eggs to flour mixture. Add lemon peel, almond extract and 2 cups of white flour to make a thick batter. Continue beating 2 minutes, scraping bowl often. With a wooden spoon, stir in 3 3/4 cups flour to make a soft dough.
Turn dough onto a well-floured surface and knead until smooth and elastic, about 10 minutes, working in more flour while kneading. Shape into a ball and place in a greased bowl, turning dough over so top is greased. Cover with a towel and let rise in a warm place, 80 - 85°F and away from any draft, until doubled.
Punch dough down. Turn dough onto a lightly floured surface. Cut dough into six equal pieces. Cover pieces with a towel & let rest for 15 minutes for easier shaping. Grease 2 large baking sheets.
On a floured surface, roll 1 piece of dough into a 24 inch rope. Repeat with remaining pieces. Place 3 ropes side by side and loosely braid, beginning in the middle and working toward each end. Place braid on baking sheet, forming a wreath. Repeat with remaining dough. Cover and let rise about 1 hour until doubled.
Preheat oven to 350°F. In a cup with a whisk, beat reserved egg white. With pastry brush, brush loaves with remaining egg white and top with poppy seeds. Place sheets on two oven racks. Bake 15 minutes. Rotate sheets between upper and lower racks so both loaves brown evenly. Bake about 20 - 25 minutes longer until golden and the loaves sound hollow when tapped with fingers. Store tightly wrapped. They can also be stored in the freezer up to 1 month.
