Lay the puff pastry directly onto the parchment. With a knife, lightly score a border about 3/4 inch in from the edge, being careful not to cut all the way through.
3 Drizzle about 2 tbsp honey over the area inside the scored border and spread it into a thin layer using the back of a spoon.
4 Arrange the sliced plums over the honey, overlapping them slightly. Leave the scored border uncovered.
5 Sprinkle the plums directly with the sugar, mixed spice, and a small pinch of salt.
6 If using, brush the exposed pastry border lightly with milk or cream.
7 Bake for 25–30 minutes, until the pastry is deeply golden and puffed and the plums are soft and slightly caramelized.
8 Remove from the oven and immediately drizzle with a little more honey.
9 Scatter the chopped pistachios over the tart.
10 Let cool for about 10 minutes before slicing.
11 Serve warm or at room temperature.
