Put the chicken breasts one at a time into a freezer bag so that it lies flat. Bash with a rolling pin until the chicken is quite thin, and then take it out and slice into about 6 to 8 slices. Repeat with the other chicken breast. This is easiest done with scissors.
Put the slices into a freezer bag with the buttermilk and leave in the refrigerator to marinade for up to 2 days.
Heat the oil in a large frying pan, or preheat the oven to 425 degrees F.
Tip the cracker crumbs into a wide shallow bowl, and then shake off the excess buttermilk from the nuggets and dip them in the crumbs. Coat them well before lying gently in the hot oil, and cooking for about 2 minutes or so a side until they are golden brown. Transfer to a kitchen towel on a plate to blot the excess oil. Alternatively, you can lay the crumb-coated chicken nuggets on a lined baking sheet and bake for 15 to 20 minutes.