Lightly spray a baking dish with baking spray and dust with a little flour. Toss in the berries.
Whisk the eggs, agave, salt, and flour together in a large bowl until smooth. Add the milk and vanilla extract. Whisk until smooth then pour into the baking dish.
Bake for 45 - 50 minutes or until lightly browned and a toothpick inserted into the center comes out clean.
When you pull it put of the oven it will wiggle a bit which is completely normal. Cool on a wire rack. The flaugnarde will have puffed up a bit and will deflate while cooling.