Preheat oven to 180C/160C fan forced. Grease four 2cm-deep, 6.5cm (base measurement) round tart tins with non-stick cooking spray. Line the bases with baking paper.
Process the granola until finely chopped. Transfer to a bowl. Add the chia seeds and butter. Stir well to combine. Divide among prepared tins. Use a teaspoon to carefully press into bases and sides. Place in fridge for 10-15 minutes or until firm.
Place tart tins on a baking tray. Bake for 12 minutes or until cases are light golden. Use a teaspoon to gently press the bases and sides of cases to flatten. Set aside to cool slightly.
For the filling, whisk the sugar, custard powder, sour cream, cream and vanilla in a bowl until smooth. Divide among cases.
Spoon the jam into a plastic piping bag or a sealable plastic bag. Cut 1 corner to make a small hole. Pipe small dots of jam around the edge of each tart, allowing 1cm intervals between each. Carefully drag a fine skewer through the centre of the jam dots to create ‘hearts’. Bake for 10-12 minutes until just set. Cool completely. Place in the fridge for 30 minutes or until firm. Use the point of a sharp knife to carefully remove from tins.
