Preheat oven to 350 degrees F. Coat a 12-cup Bundt pan
, preferably nonstick, with cooking spray and dust with flour
(or use cooking spray with flour).
Whisk whole-wheat flour, all-purpose flour, poppy seeds, baking powder, baking soda and salt in a medium bowl. Combine buttermilk, oil
, vanilla, lemon zest and lemon juice in a glass measuring cup
Beat eggs, egg whites and sugar in a large bowl with an electric mixer on high speed until thickened and pale, about 5 minutes.
Fold the dry ingredients into the egg mixture with a rubber spatula, a third at a time, alternating with 2 additions of the buttermilk mixture. Scrape the batter into the prepared pan, spreading evenly.
Bake the cake until the top springs back when touched lightly and a toothpick inserted in the center comes out clean, 35 to 40 minutes. Let cool in the pan for 5 minutes, then turn out onto a wire rack.
To prepare glaze: Sift 3/4 cup confectioners' sugar into a small bowl; mix with lemon juice and water to create a thin glaze. Poke 1-inch-deep holes all over the cake with a skewer. Coat the warm cake with the glaze using a pastry brush. Let cool completely. To serve, set the cake on a serving plate and dust with confectioners' sugar.
Note: Whole-wheat pastry flour is milled from soft wheat. It contains less gluten forming potential than regular whole-wheat flour and helps ensure a tender result in delicate baked goods while providing the nutritional benefits of whole grains. Store in the freezer. Sources: Available in large supermarkets and in natural-foods stores, and from King Arthur Flour, (800) 827-6836, bakerscatalogue.com, and Bob's Red Mill, (800) 349-2173, bobsredmill.com.
Tips: Toast poppy seeds in a small dry skillet over medium heat, stirring constantly, until fragrant, 3 to 4 minutes. Transfer to a plate to cool.
No buttermilk? You can use buttermilk powder prepared according to package directions. Or make "sour milk" the ratio is 1 tablespoon lemon juice or vinegar to 1 cup milk.
To bring cold eggs to room temperature quickly, place in a mixing bowl
and set it in a larger bowl of warm water for a few minutes; the eggs will beat to a greater volume.
To separate eggs safely: Use an egg separator, an inexpensive gadget found in cookware stores; separating eggs by passing the yolk back and forth between pieces of eggshell or your hands can expose the eggs to bacteria.
MAKE AHEAD TIP: Equipment: 10-inch (12-cup) Bundt pan, preferably nonstick
cal. (kcal) 215,
Fat, total (g) 6,
chol. (mg) 27,
sat. fat (g) 1,
carb. (g) 38,
Monosaturated fat (g) 2,
fiber (g) 2,
pro. (g) 5,
sodium (mg) 146,
Potassium (mg) 70,
Other Carb () 2.5,
Percent Daily Values are based on a 2,000 calorie diet