In a saucepan over medium heat, combine the berries, sugar, lemon juice, lemon zest, cardamom, salt, and cinnamon.
Let it simmer for about 5-10 minutes, stirring occasionally.
Scoop out about 1/2 cup of the berry juice into a bowl and mix it with the cornstarch until it’s smooth.
Pour the cornstarch mixture back into the pot with the berries and simmer for another 2-5 minutes until it thickens up nicely.
Stir in the butter until it melts, then let the mixture cool for around 5 minutes.
Pour the filling into your par-baked pie crust.
Sprinkle the cardamom crumble on top.
Pop it into the oven at 400°F and bake for about 40 minutes until it’s golden brown and bubbling with deliciousness.
Once it’s done, resist the temptation and let it cool for a few hours before you dive in.