For the cake: 

Preheat oven to 350°F

Spray a 13×9 baking dish with non-stick cooking spray.

In a medium mixing bowl, add oil, sugar, eggs, and vanilla and stir until combined

In a smaller bowl, mix together flour, baking powder, baking soda, and salt

Mix the flour and buttermilk into the sugar mixture, alternating flour and buttermilk and stir just until combined.

Pour the batter into the baking dish.

Bake for 25-28 minutes or until a toothpick inserted into the center comes out clean – the top of the cake will be a golden brown.

Let cool in pan and then cut into squares

For the trifle: 

When ready to assemble the trifle, pour the heavy cream into a bowl and using a hand mixer or a stand mixer, whip on high until thick and stiff peaks form (when you can take the beater or whisk away and the cream is thick and stands on its own). 

Cut the strawberries into slices. 

Assemble the trifle: Layer in this order – Half of the cake on the bottom, half of the cream, half of the strawberries and half of the blueberries…repeat. 

Keep in the refrigerator until ready to serve