Make the Streusel

1.  Mix the flour, brown sugar, salt, and apple pie spice together in a small bowl.
2. Add in the melted butter and stir to form crumbs.
3. Scrape the bottom of the bowl so that the crumbs don’t freeze to the bowl too hard. Place the bowl in the freezer.

Prep

1.  Preheat the oven to 350 F (180 C). Butter the sides and bottom of a springform

   (Affiliate)

   pan and then line the bottom with a piece of parchment

   (Affiliate)

   .  You can place the ring around the piece of parchment

   (Affiliate)

   and simply cut away the excess parchment

   (Affiliate)

   outside the ring for a super secure, lazy way to line your pan!
2. Wash the plums. Cut each one into thin slices–about 8-12 per plum. On most plums it is easier to pop out the pit after cutting around it as you cut them into slices. A paring knife is your best tool here.
3. Add the plums to a bowl as you cut.
4. Taste the plums, adding 1-2 tablespoons of sugar if they seem too tart to you.

Make the Batter

1. Beat the butter and sugar until smooth. 
2. Add in the egg, sour cream, and amaretto and beat until just combined.
3.  Mix the flour, almond flour, baking powder, salt, and apple pie spice together in a small bowl.
4. Add the dry ingredients to the butter mixture, stirring just until the flour disappears.

Assemble the Cake

1. Scrape the batter into the springform

   (Affiliate)

   .  Use an offset spatula

   (Affiliate)

   or spoon to smooth the batter into the pan in one even layer.
2. Take the streusel out of the freezer and scatter a little more than half of the streusel on top the batter. Place the plums in neat concentric rings on top of the cake.
3. Scatter the rest of the streusel on top the plums.

Bake the Cake

1. Bake for 50-55 minutes until the streusel is golden brown and a toothpick inserted into the cake comes out clean.
2. You can serve the cake warm or at room temperature with some powdered sugar, a dollop of whipped cream, or a scoop of ice cream.
3. The cake is best the day it’s served, but you can keep it at room temperature for up to 2 days.  Warm up leftovers in a 300 degree oven for about 5 minutes.