Prepare pastry shell as directed and blind bake up to 2 days in advance.
Preheat oven to 180℃ and line a ceramic baking dish with paper.
Prepare plums as directed and place into a large bowl with sugar, juice, 1 tbsp vanilla bean paste and the split vanilla bean. Toss gently to coat the plums with other ingredients. Allow to rest whilst oven heats.
Pour plums into the prepared baking dish and roast for 20-30 minutes until fragrant and soft, but still holding their shape. (This will vary slightly depending on the variety of plums used.)
Reserve the syrup from the plums and allow plums to cool completely. This also can be done up to 2 days in advance.
To prepare mascarpone cream, place mascarpone, the remaining vanilla bean paste and maple syrup into TM bowl and whip 10-20 sec/Butterfly/speed 4 or until holding stiff peaks. (Don’t over whip as it will separate.)
Fold in the sour cream by hand until well combined.
Spread the cold pastry shell with mascarpone mixture, top with the plums ensuring you have plenty of reserved syrup to drizzle over the top.
Dust with lavender icing sugar if you wish.
Serve immediately with ice cream if desired!
Lavender icing sugar is as easy to make as blending a few organic, dried lavender flowers with some raw sugar until powdery and fragrant.