Process the chopped cold butter, oats, almond flour, brown sugar, granulated sugar, salt, and cinnamon. If you don’t have a processor, place them in a medium bowl and toss them with your fingertips to combine. Let rest the crumble in the freezer.
In a large bowl place the plums, corn starch, and lemon juice, and mix.
Place the plum mixture into the desired molds. I used individual ramekins, but you can also use a baking dish, 8” square pan, or a 9-in. pie plate.
Let rest for 10 minutes and then, sprinkle the oat mixture over the plums. End it up with the sliced almond.
Bake at 350° F for about 40 minutes, until the topping is golden brown and the plums are tender.
Serve warm and if desired with whipped cream or a scoop of ice cream.
Notes
Storage: keep leftovers in the refrigerator for 3 days, covered in plastic wrap or an airtight container. I don't recommend freezing it.