Ingredients for the filling:
For the Batter:
Combine the shallot, onion, olive oil, lemon juice, mascarpone, egg, and salt in the bowl of a food processor. Pulse a few times to finely chop the ingredients and combine.
Place the filling in a medium size bowl, and with the utmost of care, gently fold in the crab meat being very careful not to break it up too much. Adjust the seasoning, cover, and refrigerate the filling for 1/2 hour.
In a shallow dish or bowl whisk together the seltzer water, flour, baking powder, and salt.
Heat 2 inches of EVOO up to 350 F. in a heavy bottom pot or pan.
Make sure the blossoms are clean of debris. Gently remove the flower stamens. Using a spoon, gently fill each blossom with approximately 1 heaping tablespoon of chilled crab filling. Gently twist the ends of the petals to seal. Swirl each filled blossom in the batter rotating it in the same direction that you twisted the petals so as not to undo your blossom. Place in the heated oil and fry each blossom for approximately 2 minutes, turning once until light golden brown on all sides.
Remove the blossoms from the oil to a rack to drain. Serve warm.