Preheat the oven to 350 degrees F. Spray an 8×8 inch pan liberally with nonstick spray.
In a large bowl, whisk the boiling water and cocoa powder until combined. Whisk in the chopped chocolate until melted, then whisk in the olive oil. Whisk in the egg, yolks and vanilla extract until combined. Whisk in the sugar until combined. Use a rubber spatula to fold in the flour and 1/4 teaspoon salt, stirring until the flour is just mixed in. Stir in the chopped truffles.
Bake the brownies for 32 to 38 minutes, or until the middle is set. Sprinkle the top with the flaked sea salt Let the brownies cool completely before cutting – in fact, I really like putting them in the fridge. If you cut them while they are still warm or even at room temperature, the truffles are melty (and delicious) – but sightly messy! I love keeping these in the fridge overnight before serving.