Cream the softened butter with confectioner's sugar until smooth and fluffy. Add in the egg and mix. Gradually incorporate almond meal and salt, then add plain flour until just combined. Shape into a disk, wrap in plastic, and refrigerate for one hour.

Preheat oven to 160°C (325°F). Roll out the chilled dough and line a 9-inch tart pan, pricking the bottom with a fork. Freeze for 15 minutes, then bake for 20-30 minutes until golden brown. Cool completely.

Heat the milk and vanilla in a saucepan until just boiling. In a bowl, whisk together eggs, sugar, and cornstarch. Gradually pour the warm milk into the egg mixture while whisking. Return to heat and cook until thickened, about 5 minutes. Cool in the fridge.

In a pot, combine water and sugar over medium heat until dissolved. Add rhubarb, lemon juice and peel, cinnamon stick, and star anise. Simmer for 5-10 minutes, then mash slightly and cool completely.

Spread the custard over the cooled tart shell, then layer the rhubarb compote on top. Refrigerate for at least 1 hour before serving.