Pre-heat your oven to 370℉/180℃. Line an 8″ Square Pan with greaseproof paper.
In a small bowl, break up the white chocolate and melt in the microwave in 20 second intervals, stirring in between to make sure it doesn’t burn. Alternatively do this using a double boiler: Place the chocolate in a heat proof bowl resting on a small saucepan with simmering water. Stir until melted.
In a large mixing bowl, whisk together the melted butter and both sugars. Add in the eggs and vanilla extract and mix again.
Whisk in the melted white chocolate until fully incorporated. Add the flour and fold to combine. Pour into the lined dish.
Pour the caramelized apples over the top of the blondie batter.
In a separate bowl, make the crisp topping by mixing all the ingredients together until it resembles slightly wet sand. Sprinkle this over the apples.
Bake 35-40 minutes until the topping looks just golden and the blondie looks firm (isn't wobbly). Let cool.
Make the glaze by mixing the icing sugar with just a splash of milk (start with the smallest drizzle and add more until you reach a runny consistency). Use a spoon to drizzle this over the blondies. Slice and serve!