Prep. Place unsalted butter (1/2 cup) in the freezer for 30 minutes before starting. Grate butter using a box grater and place back in the freezer for 10 minutes. Preheat oven to 375 F and line an 8" square baking dish with parchment paper.
Combine. In a medium bowl, combine almond flour (2 1/2 cups), granular erythritol (1 1/4 cup), and salt (1/4 teaspoon). Add butter and mix until butter is well coated. Remove one cup of the butter/flour combo and place it in the fridge. Add baking powder (1 tablespoon), psyllium husk (1/4 cup), heavy cream (1/2 cup), vanilla ( 1 teaspoon), and eggs (4). Combine using an electric mixer until the batter is completely smooth.
Assemble. Add cinnamon (2 teaspoons) and chopped pecans (1 cup) to the flour combo we set aside, and toss until well combined. Pour half the batter into the prepared baking dish, then half the pecan combo, then the rest of the batter, and the rest of the pecans. Press lightly to adhere the crumb topping.
Bake + enjoy! Bake in preheated oven for 35 minutes. Remove from oven, and cover the cake in foil (this will prevent the top from burning). Return to the oven and bake for another 45 minutes. Allow the cake to cool completely in the pan before removing it. Enjoy!