Preheat the oven to 350°F. Grease a 9-cup Bundt pan.

In a large bowl, whisk together the peanut flour, almond flour, oat fiber, whey protein isolate, baking powder, and salt; set aside.

In a separate mixing bowl, use a hand mixer or a stand mixer to cream the butter and sweetener. After the butter has lightened in color, it is well mixed. If the butter becomes grainy looking, it is too warm; place the bowl in the refrigerator to chill for a bit.

Add the cream cheese and peanut butter to the butter mixture and mix until smooth. Add the eggs one at a time, beating well after each addition. Add the vanilla extract and mix well.

Stir the dry ingredients into the butter mixture by hand. Stir in the chopped chocolate, if using.

Pour the batter into the prepared Bundt pan and bake for 40 to 50 minutes, until a toothpick inserted in the center comes out clean. Let cool in the pan.

Before serving, drizzle the ganache or chocolate syrup over the cake.