Place over medium heat and cook for 4–6 minutes, stirring occasionally, until the berries begin to burst and release their juices. At this point, if there are any big chunks, it should be soft enough to smush down (I like to use a potato masher).

Add the arrowroot into the berries and cook for another 30-60 seconds, until glossy and thickened.

Combine the brown cane sugar, flour, cinnamon, and salt in a large bowl. Add in the chilled butter and use two forks (a food processor, potato masher, or hands) until the crumble mixture is formed with pea-sized chunks. Refrigerate until ready to pour the cake into the pan.

Preheat the oven to 350°F (177°C). Line a 9-inch pan (square or round) with lightly oiled parchment paper or directly oiled the pan.

Whisk the flour, baking powder, baking soda, and salt together in a medium bowl. Set aside.

In a large bowl, beat the butter and cane sugar together, using a handheld or stand mixer, on high for 3 minutes until smooth and creamy. Add in the eggs and vanilla, and beat until combined. Repeat with the sour cream. Scrape down the sides and up the bottom of the bowl with a silicone spatula and beat again as needed to combine. The batter might be lumpy, this is fine.

Add the flour mixture to the wet ingredients and beat on low speed until combined. Lastly, add in the milk. You can switch to a spatula to ensure the batter is not overmixed. It should come out as a thick batter.

Again, make sure the compote is completely cool before folding into the batter. Putting it into the fridge or freezer can help speed up this process.

Pour the cake batter into your pan, followed with the berry compote. Gently swirl the two layers together until there are jammy ribbons throughout the cake. Alternatively, you can switch between pouring in bits of the batter and compote (like 5-6 times) to ensure the layers don’t mix too much together.

Sprinkle the crumble mixture evenly on top, making sure all the cake batter is covered and only a thick crumble layer is visible on top.

Bake for around 50-60 minutes. This cake is harder to tell when fully baked: it will be done when the crumble is more golden brown, there is visible height growth, and firmness (no jiggle when shook or tapped).

Once baked, remove from the oven and let it cool in the pan for 10-15 minutes on a wire rack.

Remove the cake from the pan or slice the cake while it's still in the pan. Best serve while warmed.