Preheat the oven to 350°F. Grease an 8″ square baking dish or pan. Line with parchment paper so that the ends hang over the edge by about an inch. If you have metal clamps, they will help hold the ends secure while you add layers.

Cream the butter with the brown sugar, cinnamon and salt with a hand held or stand mixer. Add in the flour, oats and coconut until combined and the mixture holds together in clumps. Reserve 1/3 or less of the mixture for the top crumble and set it aside.

Take the remaining 2/3 or more of the mixture and spread it evenly over the bottom of the prepared baking pan. Gently pack it down into an even layer. Place the pan in the freezer for 10 minutes to firm and chill.

Bake for about 15 minutes or until the bottom crust begins to lightly brown. Set aside to cool slightly.

While the base bakes, work on the cheesecake layer. In a large bowl, cream the cream cheese and sugar together until smooth and creamy. You can use a stand or hand held mixer. Add in the sour cream, heavy cream and vanilla extract; mix until smooth. Continue mixing as you add the eggs. Lastly, sift the arrowroot or corn starch overtop and mix until just combined. At this point, be careful to not overmix.

Pour the cheesecake layer over the partially baked crust and spread into an even layer. You can do this by gently tilting the pan till the cheesecake is smooth on top.

Stir together the rhubarb, strawberries, sugar and arrowroot or tapioca starch in a medium bowl. Reserve about 1/4 cup of the mixture and spoon the remaining fruit evenly over the cheesecake.

Sprinkle the remaining crumble over the fruit. Form some of the crumble into smaller pieces, and other into medium bits, to create a rustic craggy surface. Gently place the remaining fruit into the crumble, spacing it around.

Return the pan to the 350°F oven and bake for another 35 to 45 minutes, until the crumble is browned, and the cheesecake layer is mostly set. The outer edges should be set with a slight jiggle in the very center.

Let the pan cool on a wire rack, then transfer the pan to the fridge for at least four hours or overnight.

Use the parchment paper wings to transfer the cake to a cutting board. Use a sharp serrated knife to cut through just the top layer of crumble. The serrated knife works well if you use a gentle back and forth sawing motion so that the crumble doesn't get pushed down into the cheesecake. If you like, you can then switch out the knife to cut the cake into 16 squares.

Store in a sealed container in the fridge for up to five days.