Preheat your oven to 350°F (175°C) and line an 8x8-inch square baking pan with parchment paper, leaving overhang handles on the sides. Or you can just lightly butter/oil the pan.
In a large mixing bowl, thoroughly whisk together the all-purpose flour, sprouted oat flour, baking powder, baking soda, sugar, and fine sea salt until uniform and lump-free.
Pour the plant milk, vanilla extract, apple cider vinegar, and melted butter (or your choice of avocado/vegetable/canola oil) straight into the center of the dry flour mixture.
Fold gently with a silicone spatula or large mixing spoon just until a thick, uniform batter forms, being careful not to over-mix.
Gently fold in the floured blueberries and half of the dark chocolate chips (1/4 cup) until just distributed.
Spoon the thick batter into your prepared baking pan, level out the top with your spatula, and scatter the remaining 1/4 cup of chocolate chips and a few extra berries evenly across the top.
Bake at 350°F for 30 to 33 minutes until the top is golden brown and a toothpick inserted into the exact center comes out completely clean.
Remove from the oven and let the cake cool in the pan for 15 minutes to allow the delicate structure to fully set before slicing into 9 generous squares.