Line a 10-inch (26 cm) shallow tart pan with the puff pastry, covering the bottom and sides. If using a square sheet, trim and patch as needed to cover the pan. Prick the bottom all over with a fork and set aside. Preheat the oven to 350°F (180°C).

In a bowl, combine the eggs and sugar (or erythritol or other oven-safe sweetener). Mix well with a whisk or fork until smooth, but do not overbeat—you don’t want to add too much air.

Add the ground almonds and mix well. Pour in the rum or brandy, if using, and mix again until combined.

Pour the mixture into the prepared pan, spreading it evenly. Sprinkle sliced almonds over the top to cover the entire surface.

Remove the tart from the oven and place it on a wire rack. Brush the syrup over the surface of the tart while it’s still warm.