Lay your Sicín Sásta chicken fillets between two sheets of parchment paper, use a heavy rolling pin to bash the thickest part of the fillets to about 2cm thick.
Arrange fillets in a bowl or dish and pour over the buttermilk. Turn the fillets so that they’re coated, then push down so they’re submerged. Cover and leave in the fridge to tenderise for at least 2 hours, but leaving overnight is best.
Whisk together the flour and spicebag mix, spread onto a plate.
Fill a large pan with about 3cm of sunflower oil, heat over medium high heat.
While oil is heating, remove chicken from buttermilk (discard the buttermilk), and coat each fillet well with the seasoned flour. To check that the oil is hot enough, the surface should have a slight rippling effect, dip a wooden skewer into it, if it starts to bubble on the skewer it’s ready.
Carefully place two of the chicken fillets into the oil and cook for about 4 minutes on both sides, they should be golden brown and cooked through. Leave cooked fillets on plate with paper towel while you cook the remaining two fillets. (If they brown too quickly, lower heat, you can also add another drop of oil to help cool it quicker.)
To serve, mix together coleslaw ingredients, spoon onto bottom half of bun, then top with chicken fillet, a good dollop of mayonnaise, then the top of the bun.
Serve with potato wedges and ketchup.