Preheat oven to 350°F Place a cooling rack on a baking sheet & spray with cooking oil.
In a gallon ziptop bag, slightly crush rice krispies - not crushed into a powder.
On one plate, place dry chicken breast pieces. On another plate, combine flour with salt & dried tarragon. In a shallow dish, lightly whisk egg whites. On another plate, place crushed rice krispies.
Dip each piece of chicken, one at a time, into the egg whites, then dredge in flour, then re-dip in the egg whites, then dredge in the rice krispies. Place on rack on baking sheet. Bake for 15 - 20 minutes until cooked through.
In a large skillet, heat oil. Add shallots & saute 3 minutes. Add chicken broth & blueberries. If using dried tarragon, add now. Bring to a boil & simmer until thickened about 15 - 20 minutes. Off heat, add mascarpone cheese & fresh tarragon, if using.