Preheat oven to 375°F. Using a sharp knife, score a line around the edge of the pastry sheet about 1 inch from the edge, be careful not to cut all the way through the dough. Keeping inside the scoring line you just made, arrange the pear slices in one layer on top of the pastry. It may seem as though there isn't enough pear there and you may want to add a lot more - don't.
Hold your ground! Noting worse than soggy puff pastry! Scatter the bits of blue cheese evenly over the pears, followed by the walnut halves. Dot the pieces the tart with bits of the salted butter. Place in the oven and bake for 12 - 15 minutes until the pastry is golden and cooked through and the cheese melted. Served hot or warm, with a salad, makes a great lunch.