Method
1. Pre-heat oven - 175°C / 350°F
2. Grease the pan with some butter
3. Add granulated sugar, egg and egg yolk to a clean large mixing bowl
4. Whisk until thick - approx 5 min
5. Add all purpose flour, baking powder, ground cinnamon and salt to a clean medium bowl
6. Whisk briefly until combined
7. Transfer dry ingredients to batter bit by bit and mix
8. Add unsalted butter to a clean small bowl
9. Melt in microwave - low heat
10. Add melted butter to the batter and mix gently until just combined
11. Transfer batter to tart pan
12. Arrange the plum pieces evenly
13. Bake until lightly browned - 40 min, 175°C / 350°F
14. Dust with powdered sugar
15. Leave in pan until completely cool