Make the compote first, since it needs time to chill before you can stir it into the ice cream. In a small saucepan on low heat, combine the frozen blueberries and sugar. Stir often till the berries begin to release their juices and thaw. Continue to let them cook for 3 to 4 minutes.
Once the liquid is very lightly simmering and the berries have softened, sprinkle the cornflour over it and stir it in thoroughly.
Cook for another 1 to 2 minutes until the mixture begins to thicken and coat the back of the spoon. Take it off the heat and let it cool for 20 minutes at room temperature. Then transfer to the fridge for at least an hour. It will thicken further as it chills.
Now make the crumble. Preheat the oven to to 170 C and line a baking tray with a silicone mat or non-stick baking paper.
Combine the flour, sugar, salt and cinnamon in a bowl. Stir well, then add the cold, cubed butter. Rub it in with your fingertips until the flour is no longer dry and the mixture clumps together when you press it between your fingers.
Tip the crumble onto the prepared tray and spread it out in an even layer, making sure the clumps stay as is, so that they add more texture to the ice cream.
Bake for 5 to 7 minutes, stirring the crumble halfway through, until toasty and golden-brown. Set aside to cool completely.
Now make the ice cream base! Using a hand mixer, or a stand mixer, whip the cream on high speed (see notes) until it thickens and forms stiff peaks with only slightly rounded tips.
Stir in the condensed milk gently. Then stir in the chilled blueberry compote. You can leave it a little swirly, or stir it in completely to get a nice purple colour.
Finally, gently fold in the crumble. By this time the cream would have deflated a bit, so don't be too vigorous. Pour into a freezer-safe container with a tight fitting lid, or use a metal loaf tin and cover it with clingfilm. Remember to scrape the bottom of the bowl while because the berries will sink down.
Freeze for at least 12 hours for the best texture, especially in hot climates. I found it most easy to scoop after 48 hours. The ice cream does melt pretty quick, but all the more reason to eat it really fast! Will keep in the freezer for about 10 days. Happy summer :)