Preheat your steam oven to 375°F/190°C, combination steam setting. If your oven has variable steam settings, use 60%. If not, don't worry! Just set to combi steam at the correct temperature and the oven will take care of the humidity. Line a baking sheet with parchment paper and set aside.
Scatter about a third of the cheese over your counter in a space the size of your pastry sheet. Lay the pastry over the top and scatter another third of the cheese on top.
1 1/2 cups grated cheese, 1 sheet puff pastry
Roll out the pastry so it's about 1/8in (3mm) thick. This will press the cheese into each side as you flatten it.
Fold the pastry sheet in half and sprinkle with the remaining cheese, then roll again to make it 1/8in (3mm) thick. The dimensions don't matter too much here, but do try to keep the pastry in a rectangle or square shape so it's easier to cut full straws from it.
1 1/2 cups grated cheese
Cut the pastry into strips about 1 inch (2.5cm) wide. Make them as long or short as you like; I prefer mine roughly 6-8 inches (15-20cm) long.
Transfer each strip to the prepared baking sheet. As you pick it up to move, twist the ends to make a long spiral. You may need to press the ends down onto the paper to stop them untwisting as you put each one down. Leave a gap of at least 1 inch (2.5cm) between each strip.
Chill the prepared straws for at least half an hour or up to a day (see notes) before baking. Baking them from cold makes the pastry puff and separate much better than from room temperature.
Bake the straws until they're golden brown, puffed and flaky, about 15 minutes. Cool on the baking sheet and serve warm or at room temperature.