Place 350g frozen raspberries and 1 tbsp lemon juice in a small saucepan and heat through until the raspberries start to cook. Bash them gently with the back of a wooden spoon so that they start to break down and become sauce-like.
Remove from the heat and stir in 3 tbsp maple syrup or honey and 4 tbsp chia seeds.
Leave to cool, then transfer to a container and put in the fridge to set for an hour or two.
To make the pastry rub 100g cold butter into 225g spelt flour with your finger tips, or in a food processor, until you have a breadcrumb-like consistency. Gradually add the water, a tbsp at a time and mix until you have a firm dough. Wrap in cling film and chill for 30 minutes.
Pre-heat the oven to 180°C (fan)/200°C/gas mark 6.
Grease a small bun tin (one that you use for fairy cakes or mince pies is perfect).
Lightly flour your work surface and roll the pastry out to a thickness of around 5mm. Cut out 12 rounds and press them into the bun tin. Lightly prick each one with a fork. You will probably have a bit of pastry left over. You could either make extra tarts, make some lids for your tarts or freeze it for next time. Little heart shaped lids would make these a perfect healthy treat for Valentine's Day.
Fill each pastry case with your raspberry jam and bake in the oven for 15-18 minutes until the pastry is cooked through.
Allow to cool in the tin for 10 minutes before removing and allowing to cool completely on a wire rack.