Cook raspberries in a pan on medium heat for a few minutes until they soften and break down. Press with the back of a spoon to help the process.
Remove from the stove and add the rest of the ingredients. Mix well and pour into a jar. Leave to cool, cover with a lid and keep in the fridge.
Tart Shells
Add butter and sweetener into a bowl. Using a spatula, mix everything together. Now add the egg yolk and vanilla extract. Continue mixing. Finally, add flour and bring everything together into a dough.
Cover with cling film and chill in the fridge for 30 minutes or until it's manageable.
Take a piece of dough and press it evenly into a 2.5-inch (6.5 cm) tart mould. Cut off excess dough with a knife. Using a fork, prick the base so that it doesn't puff up while baking. Repeat the same with the rest of the dough. Place them on a baking tray. Place them in the freezer for 10 minutes.
Bake
Spoon some jam into the tart shells until ¾ full. Bake in a preheated oven at 350ºF (175ºC) using the conventional mode, on a lower ⅔ rack for 25 minutes or until the shells are golden.
Remove from the oven, and leave to cool for 10 minutes. Flip and tap the bottom of the tart moulds to release the tarts. Cool completely on a rack. Chill in the fridge for a few hours before serving (that's how I like them!)
Notes
The tarts are a bit fragile when they're hot, so handle them gently.