Preheat oven to 350℉.
Grease and line a 9" springform pan with parchment paper, or use a 9" x 9" baking dish.
Cream together butter and sugar until light and fluffy, about 3-4 minutes, using either a handheld mixer or stand mixer with paddle attachment.
Add honey to the sugar mixture and mix until well incorporated.
Add eggs, vanilla, and ginger until also well incorporated.
Sift flour, baking powder, salt, and cardamom together. Slowly add dry ingredients to the wet ingredients, and mix until just incorporated. Be careful not to over-mix.
Pour the batter into the lined and greased cake pan. Add the sliced plum on top of the cake. They will sink as they bake.
Top with generous sprinkling of Turbinado/raw sugar.
Bake 35-40 minutes, or until a cake tester comes out clean when tested in the center of the cake.
(Optional) Heat ¼ cup of honey until warm and brush on top of the cake once it has cooled.
