Add the berries directly to the dry ingredients and gently toss until they are fully coated in flour. This prevents the berries from sinking to the bottom of the pan while baking.
Pour in the vegetable oil, sour cream, eggs, and vanilla extract. Mix with a whisk until just combined and no lumps of flour remain. Do not overmix.
Pour the cake batter into your prepared 9-inch cake pan. Smooth the top with a spatula and scatter a few extra berries over the top.
Bake for 55-60 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs.
Let the cake cool in the pan for 15 minutes, then carefully remove it and place it on a wire rack to cool to room temperature. Dust with powdered sugar.
Notes
Coat Your Berries: Tossing your berries in the flour mixture before adding the liquids is essential to stop them from sinking to the bottom of the cake.
Use Room-Temperature Ingredients: Ensure your eggs and sour cream are at room temperature before starting. Cold ingredients can cause the batter to seize, leading to an uneven bake.
Don't Overmix: Mix the batter until the flour just disappears. Overmixing develops the gluten in the flour, which makes the cake dense and dry instead of light and fluffy.
Line Your Baking Pan: Always use parchment paper. It helps the cake bake evenly and guarantees a clean release from the pan.
Measure Your Flour Correctly: Avoid scooping flour directly with a measuring cup. Instead, fluff the flour with a spoon, scoop it gently into the cup, and level it off with the back of a knife.
Get Creative with Mix-ins: Make this recipe your own by adding chocolate chips, chopped walnuts, pecans, or banana slices along with the berries.
Be Patient: It is tempting to slice the cake straight out of the oven, but letting it cool for at least an hour allows the crumb to set so it won't crumble apart when cut.