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Preheat the oven to 350°F. Spray a 9-x-5-inch loaf pan with nonstick spray. Line the bottom with a rectangle of parchment. Dust the sides with flour and tap out the excess.
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Pulse the cranberries in the food processor until they are coarsely chopped. Set aside.
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In a large bowl, whisk the all-purpose flour, whole wheat flour, sugar, baking powder, baking soda, salt, and orange zest.
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In a small bowl, whisk the orange juice, kefir, butter, egg, and vanilla extract. Pour the wet ingredients into the dry and stir just until blended (don't over-mix). Fold in the cranberries.
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Spread the batter evenly into the prepared pan and bake until a toothpick inserted in the center of the loaf comes out clean, 45 to 55 minutes. Cool the cake in the pan for 20 minutes, then turn it out and cool completely on a wire rack.
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To make the glaze, combine the confectioner's sugar, orange juice, and vanilla in a small bowl and whisk until smooth. Place the cake, still on the cooling rack, over a baking sheet lined with wax paper. Drizzle the cake with the glaze and let stand until hardened, about 30 minutes.