Bring the vegetable stock and two tarragon sprigs to the boil in a medium saucepan over medium–high heat.
Blanch the broad beans for 2 minutes then, using a slotted spoon, remove from the stock and immediately transfer to a bowl of iced water. Remove the outer skins of most of the larger beans, leaving the smaller ones intact for a touch of bitterness.
Bring the stock back to the boil and blanch the peas for 4 minutes, then strain and cool in the iced water.
Finely chop the remaining tarragon leaves and place in a medium bowl with the blanched broad beans and peas, mint, a pinch of salt and pepper and half the olive oil.
In a separate bowl, combine the vinegar, ginger, lemon juice and remaining oil, then toss through the shredded radicchio. Mix this through the broad bean and pea mixture.
Transfer the salad to a serving platter and dot the queso fresco or ricotta over the top.