Preheat oven to 180°C.
Grease a bundt pan and set aside.
Peel, core and dice the apples. Stir in cinnamon and set aside.
In a large bowl, whisk together the almond meal, coconut flour, protein powder, baking powder, salt and xanthan gum. Set aside.
In another bowl, cream together butter and sweetener. Beat in eggs and milk. Then, using a rubber spatula, add in flour mixture and mix until well combined.
Spread batter into prepared bundt pan, using the back of spoon to smooth it out. Distribute apple evenly and press the pieces into the batter.
Bake ca. 40 minutes or until inserted toothpick comes out clean.
Serve warm or cold, plain or with (sugar-free) whipped cream, ice cream or vanilla sauce.
* Tagatesse is twice as sweet as regular sugar. If using sugar or another sweetener, keep that ratio in mind.
**Can be swapped for other types of milk.