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.
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.