Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.
In a medium bowl, whisk together flour, baking powder, baking soda, and salt.
In a large bowl, cream together butter and sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla.
Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined.
Gently fold in the blueberries.
Pour batter into the prepared pan and bake for 35-40 minutes, or until a wooden skewer inserted into the center comes out clean.
Let cool completely before serving.
Notes
This cake is best served fresh, but can be stored in an airtight container at room temperature for up to 3 days.