Portuguese Chocolate Tarts

5 ounce (150 gram) slab puff pastry
1 egg yolk
2 tablespoons caster sugar (superfine sugar)
Pinch allspice
A couple pinches cinnamon
1 orange, zested
For the filling:
5 1/2 fluid ounces (160 millilitres) double cream (heavy cream)
2 level tablespoons caster sugar
The smallest pinch salt
1/2 stick butter, softened
1/2 pound best-quality baking chocolate, broken up
1 1/2 fluid ounces (50 millilitres) milk
Cocoa powder, for dusting