Preheat oven to 400 degrees F. Line a baking sheet with parchment or foil and set aside. Dust your work surface with the tablespoon of flour. Roll the puff pastry to a 14-inch by 8-inch rectangle that’s about 1/8-inch thick. Trim the rectangle so the edges are straight. The accuracy of the rectangle’s dimensions isn’t vital; feel free to eyeball the measurements.
Using a sharp knife, lightly score the puff pastry dough 1-inch from the edges, making a rectangle shape within the rectangle. Take a fork and score the inside of smallest rectangle, ten or fifteen times. Transfer the sheet of puff pastry to the lined baking sheet. Brush the entire puff pastry with the lightly beaten egg and place the baking sheet in the freezer to chill for 5 minutes.
Meanwhile, core and cut the apples into 1/4-inch slices. Toss the apples with the lemon juice to avoid them from browning.
Arrange the apple slices side-by-side, creating two or three rows. Transfer to the oven and bake for 10 to 15 minutes, until the edges are golden brown and apples appear to have softened. Remove the tart from the oven and drizzle with honey and sprinkle half of the blue cheese on top. Place the tart back in the oven to warm and melt the cheese, 1 to 2 minutes.
Remove the tart from the oven and sprinkle with the reserved blue cheese and pistachios. Slice up and serve.