Preheat oven to 400 °F for muffins, mini loaves and mini Bundts or 375 °F for a large loaf. Coat pan(s) (see "Pan Options") with cooking spray.
Prepare Quick-Bread Dry Mix.
Whisk eggs, buttermilk, brown sugar, butter, oil and vanilla in a large bowl until well combined.
Make a well in the center of the dry ingredients, pour in the wet ingredients and stir until just combined. Add orange zest, cranberries and walnuts. Stir just to combine; do not overmix. Transfer batter to the prepared pan(s). Top with additional walnuts, if desired.
Bake until golden brown and a wooden skewer inserted into the center comes out clean, 22 to 25 minutes for muffins or mini Bundts, 35 minutes for mini loaves, 1 hour 10 minutes for a large loaf. Let cool in the pan(s) for 10 minutes, then turn out onto a wire rack. Let muffins and mini Bundts cool for 5 minutes more, mini loaves for 30 minutes, large loaves for 40 minutes.
Make Ahead Tip: Store, individually wrapped, at room temperature for up to 2 days or in the freezer for up to 1 month.
No buttermilk? Mix 1 tablespoon lemon juice into 1 cup milk.
To make quick work of chopping cranberries, place whole berries in a food processor and pulse a few times until the berries are coarsely chopped.
To toast walnuts, pecans or hazelnuts, spread nuts onto a baking sheet and bake at 350°F, stirring once, until fragrant, 7 to 9 minutes. To toast sliced almonds, cook in a small dry skillet over medium-low heat, stirring constantly, until fragrant and lightly browned, 2 to 4 minutes.
Each of these recipes will make:
1 large loaf (9-by-5-inch pan)
3 mini loaves (6-by-3-inch pan, 2-cup capacity)
6 mini Bundt cakes (6-cup mini Bundt pan, scant 1-cup capacity per cake)
12 muffins (standard 12-cup, 2 1/2-inch muffin pan)
Storage smarts: For long-term freezer storage, wrap your food in a layer of plastic wrap followed by a layer of foil. The plastic will help prevent freezer burn while the foil will help keep off-odors from seeping into the food.