Line a 9-inch square cake pan with parchment paper and preheat the oven to 325F.
In a medium bowl, mix together the ingredients of the topping: flour, coconut sugar, cinnamon, salt, melted butter. Stir until the mixture is well-combined and crumbly. Set aside.
In another medium bowl, whisk together the dry ingredients: flour, salt, baking powder and baking soda, until well combined.
In a large bowl using a stand mixer, cream the coconut oil and the cane sugar until light and smooth. Add the egg and the yolk.
Stir in half the dry ingredients, then the sour cream and vanilla, then the rest of the dry ingredients. Mix just until the dry ingredients are moistened without over-mixing.
Transfer the batter into the prepared pan and use a spatula to spread the batter as evenly as you can. Then sprinkle the topping over the cake batter in the pan,
Bake in oven for 45 to 50 minutes, until a toothpick inserted in the center comes out clean.
Let cool completely, then slice into squares and enjoy with coffee, if you desire