Step 1: Preheat oven to 350°F (175°C). Grease and flour a 12-cup bundt pan or a 9x13 inch baking dish. Ensure the pan is thoroughly coated to prevent sticking.
Step 2: In a large bowl, cream together the softened butter and granulated sugar with an electric mixer until light and fluffy, about 3-5 minutes. Scrape down the sides of the bowl as needed.
Step 3: Add eggs one at a time, beating well after each addition until fully incorporated. Stir in the lemon zest.
Step 4: In a separate medium bowl, whisk together the 3 cups all-purpose flour, baking powder, baking soda, and salt.
Step 5: In a small bowl, whisk together the buttermilk and 1/4 cup fresh lemon juice.
Step 6: Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk mixture. Begin and end with the dry ingredients (e.g., 1/3 dry, 1/2 wet, 1/3 dry, 1/2 wet, 1/3 dry). Mix on low speed until just combined, being careful not to overmix.
Step 7: In a small bowl, gently toss the mixed fresh berries with 1 tablespoon of all-purpose flour. This helps prevent them from sinking to the bottom of the cake.
Step 8: Gently fold the floured berries into the cake batter using a spatula until just distributed.
Step 9: Pour the batter into the prepared bundt pan and spread evenly. Bake for 45-55 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean. Baking time may vary slightly for a 9x13 inch pan (35-45 minutes).
Step 10: Let the cake cool in the pan on a wire rack for 10-15 minutes, then invert it onto the wire rack to cool completely before glazing.
Step 11: While the cake cools, prepare the cream cheese glaze: In a medium bowl, beat the softened cream cheese and softened butter until smooth. Gradually add the powdered sugar, beating until creamy. Stir in 2-3 tablespoons of fresh lemon juice until the glaze is smooth and pourable. Add more lemon juice for a thinner glaze or more powdered sugar for a thicker glaze, if desired.
Step 12: Once the cake is completely cool, drizzle the cream cheese glaze generously over the top. Garnish with extra fresh berries and lemon zest if desired. Slice and serve your delicious Lemon Berry Sunshine Cake!