How to make Coarse Plum Cinnamon Pie
1. Cut the plums in half and remove the seeds. Place a rack in the center and preheat the oven to 175 degrees. Grease a square baking sheet with butter and sprinkle with flour.
2. Mix flour, baking powder, salt and cinnamon together. Beat butter with a mixer on medium speed until soft and creamy, about 3 minutes. Add sugar and beat for another 3 minutes, then add eggs, one at a time, whisking after each addition. Add orange zest, vanilla extract and beat on medium speed until smooth. Reduce speed to low and add dry ingredients. Pour the dough onto a prepared baking sheet and smooth with a spatula.
3. Put the halves of the plums on top of the dough, you should get about 4 rows of 4 plums each. Squeeze the plums lightly into the dough. Bake for about 30-40 minutes, until honey brown.
4. Allow to cool on a baking sheet for 15 minutes - during this time the pie is soaked in plum juice. Place the cake on a large platter. Sprinkle with powdered sugar if desired. You can cover the cake and store it at room temperature for 2 days - it will stay soft and moist.