Prepare the streusel: In a medium bowl, combine almond flour remaining sweetener, cinnamon, salt, vanilla, and butter and combine well until crumbly. Refrigerate until using.
Preheat the oven to 375ºF and line 9 wells of a standard muffin tin with paper liners.
Combine the melted butter, allulose, stevia, vanilla, and egg in a large bowl. Stir in sour cream and mix until well combined. Add in the remaining ingredients and stir well to combine evenly.
Place a spoonful of batter in the bottom of each muffin tin liner, top with a spoonful of the cinnamon filling, then top with remaining batter. Finally, sprinkle the streusel evenly over the top.
Bake for 20 minutes, or until lightly golden and a toothpick that is inserted comes out clean. Cool in the pan before serving.