Preheat the oven to 300 F / 150 C.
In a large bowl, combine all of the dry ingredients. Mix.
Next, add all of the wet ingredients (no blueberries yet!). Mix until combined.
Method 1: Add in the blueberries and pour the cake batter in a greased 8x8 or 9x9 baking dish.
Method 2: Add 1/3 of the cake batter to a greased 8x8 or 9x9 baking dish, then place 1/2 cup blueberries. Repeat. Finally, top with the remaining 1/3 cake batter. This reduces how much the blueberries sink!
Bake the cake at 300 F / 150 C for 45 minutes.
Once the cake has baked and cooled, make the glaze by combining the powdered sugar, cream, and mandarin orange zest.
Pour the glaze over the top of the cake or spoon some onto each pre-cut piece.
Enjoy!