Preheat oven to 350 degrees F, 325 degrees F convection.  Oil an 8 or 9 inch square pan.

Make the crumbs.  In a medium bowl, stir together cinnamon, ginger, cardamom, salt, and flour.  Stir in oil, sugar, and syrup until clumps of various sizes form.  Set aside.

Stir the plums together with the lemon juice, syrup, ginger, and cardamom to macerate while making the cake.

Make the cake.  in a medium bowl, beat the oil and sugar until combined and slightly lightened in texture.  Beat in the egg and vanilla.  Stir in half the flour, followed by the milk, and finally the baking powder and remainder of the milk.

Spread the cake batter on the bottom of the prepared pan.  Top with an even layer of plums, covering all the cake.  Pour any juice left in the bowl over the plums.  Finish by sprinkling with the crumbs.  Bake about 1 hour.  A toothpick test is tough, so make sure it’s golden brown and the fruit juices are bubbling.  Cool completely in the pan.

Cake may be stored in an airtight container at room temperature for up to 4 days or frozen, wrapped in parchment and foil and placed in a zipper bag for up to 3 months.  Thaw in the microwave about 1 minute.