Remove puff pastry from refrigerator and let rest for 10 minutes. Roll out and spread about 3 tablespoons of sweetened condensed milk on top.
Roll up loosely from the narrow side. Cut into 1-2 cm wide slices. Place in a greased baking dish, being careful as condensed milk may drip. Pour the remaining condensed milk over the snails.
Bake at 175°C (347°F) with top and bottom heat for 20 minutes, until lightly brown.