Preheat oven to 180°C.
Melt butter in a heat-proof bowl in the microwave. Whisk egg. Add hot cross cookie mix to butter and stir with a wooden spoon to combine. Stir through egg.
Scoop heaped tablespoons of mixture and dollop onto a lined baking tray. Bake for 10-12 minutes until lightly golden. Allow to cool on a wire rack.
Melt the remaining white chocolate in the microwave on low in 20-second bursts. Use a small piping bag or a teaspoon and carefully drizzle a cross on top of each cookie. Leave to set before eating.