1. Preparation is Key:

• Preheat your oven to 350°F (175°C).
• Generously grease and flour a 9×13 inch baking pan. Alternatively, you can use two 8-inch or 9-inch round cake pans, or a 10-12 cup Bundt pan (adjust baking time accordingly – Bundt pans usually take longer). Lining the bottom of the pan(s) with parchment paper after greasing is highly recommended for easy removal.

2. Whisk the Dry Ingredients:

• In a medium bowl, whisk together the 2 ½ cups of all-purpose flour, 2 ½ teaspoons of baking powder, ½ teaspoon of baking soda, and ¾ teaspoon of salt. Whisking helps aerate the flour and ensures the leavening agents and salt are evenly distributed, leading to a more consistent rise and flavour. Set aside.

3. Cream Butter, Oil, and Sugar:

• In a large bowl, using an electric mixer (stand mixer with paddle attachment or handheld mixer), beat the ½ cup of softened unsalted butter and ½ cup of vegetable oil together on medium speed until combined.
• Add the 1 ¾ cups of granulated sugar and the 1 tablespoon of lemon zest (if using). Increase the speed to medium-high and beat for a full 3-5 minutes, scraping down the sides and bottom of the bowl occasionally. This step is crucial! Creaming incorporates air into the mixture, which creates a lighter cake texture. The mixture should look pale, light, and fluffy. Don’t skimp on this creaming time.

4. Incorporate Eggs and Vanilla:

• Reduce the mixer speed to medium-low. Add the 3 large eggs one at a time, beating well after each addition until just combined. Wait for the first egg to be fully incorporated before adding the next.
• Beat in the 2 teaspoons of pure vanilla extract. Scrape down the sides of the bowl again.

5. Alternate Wet and Dry Ingredients:

• Turn the mixer speed down to low. Add the dry ingredients mixture in three additions, alternating with the 1 cup of room temperature buttermilk in two additions. Begin and end with the dry ingredients.

  • Add approximately one-third of the dry ingredients mixture; mix on low until just combined.
  • Add about half of the buttermilk; mix on low until just combined.
  • Add another third of the dry ingredients; mix on low until just combined.
  • Add the remaining buttermilk; mix on low until just combined.
  • Add the final third of the dry ingredients; mix on low until just barely combined.

• Crucial Tip: Stop mixing as soon as you no longer see large streaks of flour. Overmixing at this stage develops the gluten in the flour too much, which can lead to a tough or dense cake instead of a tender, moist one. A few small lumps are okay.

6. Prepare and Fold in the Blackberries:

• In a small bowl, gently toss the 2 cups of blackberries (fresh or frozen – do not thaw frozen) with 1 tablespoon of flour (taken from the measured dry ingredients earlier, or use an extra tablespoon). This light flour coating helps prevent the berries from sinking straight to the bottom of the cake during baking.
• Using a rubber spatula, gently fold the flour-coated blackberries into the cake batter. Fold just until they are evenly distributed – again, avoid overmixing.

7. Pour and Bake:

• Pour the batter evenly into your prepared baking pan(s). If using a 9×13 inch pan, gently spread the batter to the edges. If using round pans, divide the batter evenly. If using a Bundt pan, ensure the batter is level.
• Bake at 350°F (175°C) for the following estimated times:

  • 9×13 inch pan: 40-50 minutes
  • 8-inch or 9-inch round pans: 30-40 minutes
  • 10-12 cup Bundt pan: 50-65 minutes

• The cake is done when a wooden skewer or toothpick inserted into the center comes out clean or with a few moist crumbs attached (but no wet batter). The top should be golden brown and spring back lightly when touched. Start checking for doneness around the lower end of the time range, as oven temperatures can vary.

8. Cool Completely:

• Place the cake pan(s) on a wire rack and let the cake cool in the pan for 15-20 minutes. This allows the cake structure to set, preventing it from breaking when you remove it.
• If using round pans or a Bundt pan, carefully invert the cake(s) onto the wire rack to cool completely. If using a 9×13 pan, you can let it cool completely in the pan. Ensure the cake is completely cool before glazing or frosting (at least 1-2 hours). Applying glaze to a warm cake will cause it to melt and slide off.

9. (Optional) Prepare and Apply the Lemon Glaze:

• Once the cake is completely cool, prepare the glaze. In a small bowl, whisk together the 1 cup of sifted powdered sugar and 2 tablespoons of fresh lemon juice.
• If the glaze is too thick, add the remaining tablespoon of lemon juice or ½ – 1 tablespoon of milk or cream, a tiny bit at a time, until you reach your desired drizzling consistency.
• Drizzle the glaze over the cooled cake. Allow the glaze to set for about 15-20 minutes before slicing and serving.