To make the cheese straws, heat the oven to gas 6, 200˚C, fan 180˚C. Line 1 large or 2 medium-sized baking trays with nonstick baking paper. Beat together the egg and milk in a small bowl. Unroll the pastry onto your work surface and brush over the egg and milk mixture. Scatter both of the cheeses over the top and press down lightly so they stick to the pastry. Using a sharp knife, cut the pastry in half and then cut each half into strips about 1.5cm wide. Carefully twist each pastry strip and place onto the prepared baking trays. Scatter any cheese that falls off over the top. Place in the oven for about 10-12 minutes, until golden and puffed up. Remove from the oven and cool on the trays. To make the dip, peel the avocado and remove the stone. Place in a bowl and mash with a fork. Add the mayonnaise and coriander along with the tomato and sweet-chilli sauce. Mix to combine and transfer to a bowl for serving, or keep in the fridge for up to 24 hours until needed.