Preheat Oven to 210CPlace oven rack just below middle of ovenPrepare muffin trays with cooking spray or cupcake casesMash the bananas well and grate the apple (including skin) and set asideIn a large bowl mix together the mashed banana, sugar, salt, oil, egg and milk until well combinedStir in the chocolate chips and grated apple and mix wellStir the flour before measuring (to lighten it) Spoon the flour into the cup without packing it or banging it down.Sprinkle the flour over the top of the other ingredients then gently fold it in without overmixing, stopping when their are no streaks or pockets of flour visibleSpoon the mixture into prepare muffin trays to ¾ fullBake for 10-14 minutes until golden brown and the tops spring back when gently touchedLeave to stand for 2-3 minutes in their pansRemove carefully and cool on a wire rack.Store in an airtight container - muffins can be frozen once cooled.