Preheat your oven to 180C/350F and line a muffin pan with paper liners. Add the room temperature butter and cream cheese to a bowl. Beat using a hand blender until incorporated.
Step 2
Add the granulated erythritol and lemon zest and beat until creamy. Add the eggs one at a time and beat until incorporated. Add the vanilla and lemon juice and beat again.
Step 3
In another bowl, mix the almond flour, coconut flour, baking powder, and salt. Add the dry mixture to the wet, and fold to form a batter. Roughly chop ½ cup of blackberries and fold them in.
Step 4
Divide the batter into the prepared muffin pan. Add the remaining ¼ cup of berries to the top of the cupcakes and press them in slightly. Sprinkle the top with some granulated erythritol.
Step 5
Transfer the pan to the oven and bake for 20-25 minutes until lightly browned and a toothpick inserted comes out clean. Transfer the muffins to a cooling rack and let cool completely. Serve warm or at room temperature.