Preheat your oven to 350°F (175°C). Set the oven rack in the middle position.
Lightly grease a loaf pan using butter or non-stick spray to ensure easy release of the bread after baking.
In a large mixing bowl, whisk together whole wheat flour, all-purpose flour, baking soda, salt, and brown sugar. Ensure all ingredients are well combined and there are no lumps.
In a separate bowl, combine the molasses, buttermilk, beaten egg, and oil. Whisk until the mixture is smooth.
Slowly pour the wet mixture into the dry ingredients. Gently stir until the batter is just combined. Be cautious not to overmix.
Transfer the batter into the prepared loaf pan, spreading it out evenly. Tap the pan gently on the countertop to remove any air bubbles. Bake in the preheated oven for about 45 minutes or until a toothpick or knife inserted into the center of the bread comes out clean.
After baking, let the bread sit in the pan for 10 minutes. Then, transfer it to a wire rack to cool completely. This ensures the bread remains soft and doesn't become soggy from the steam.
Notes
Molasses Alternative: If molasses isn't available, honey or maple syrup can be used as a substitute, although this will change the flavor profile slightly.
Buttermilk Substitute: If you don't have buttermilk on hand, combine 2 cups of milk with 2 tablespoons of lemon juice or white vinegar. Let it sit for 5 minutes before using.
Brown soda bread is delicious when served warm with butter, jam, or honey. It's also a great accompaniment to soups and stews.
Store in a cool, dry place wrapped in a cloth or plastic bag to keep it fresh. It's best consumed within 2-3 days.