Chilled pea soup with tarragon & radishes

For ➍
1 tbs unsalted butter
1 large shallot, finely chopped
30 cl (chicken) stock
salt & freshly ground black pepper
600 g shelled peas [unfrozen]
5 cl crème fraiche
1 ts finely grated lemon zest
fresh tarragon
sliced radishes

Melt the butter in a small saucepan over medium heat. Add the shallots and sauté until translucent without browning, 3-4 m. Add the broth, ½ ts salt and ½ ts black pepper and simmer 2 m. Remove from heat and cool to room temperature.
While the stock is cooling, bring a large pot of salted water to a boil. Add the peas and cook until peas are tender, 2 to 3 m. Drain and rinse under cold water or shock in ice water to prevent further cooking.
Combine the half of the cooled stock and peas in the bowl of a food processor. Process until very smooth. Add additional stock a little at a time and process to achieve desired consistency. (The soup should be a little thick and not too runny).
Transfer to a bowl, and taste for salt and pepper. Whisk the crème fraiche and lemon zest together in a small bowl. Gently stir into the peas, leaving light traces of the cream visible. 

Carefully divide among 4 serving bowls. Garnish with snipped or whole tarragon leaves and sliced radishes.