Preheat the oven to 350°F (175°C). Grease a 9-inch round or square baking pan with butter or non-stick cooking spray, and line the bottom with parchment paper.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a large bowl, beat the softened butter and granulated sugar together with a hand mixer or stand mixer until light and fluffy, about 2-3 minutes.

Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract and orange zest.

Alternate adding the dry ingredients and orange juice to the wet mixture in three additions, mixing just until combined after each addition. Do not overmix.

Gently fold in the fresh or thawed frozen blueberries with a spatula.

Transfer the batter to the prepared baking pan and smooth the top with a spatula. Drizzle the agave nectar over the top of the batter, and sprinkle evenly with the chopped pistachios.

Bake for 45-55 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs attached.

Remove the cake from the oven and allow it to cool in the pan for 10 minutes. Then, carefully transfer it to a wire rack to cool completely.

Serve the Blueberry Orange Brunch Cake warm or at room temperature, with a dollop of whipped cream or a scoop of vanilla ice cream if desired.