1 tablespoon heavy cream (may substitute full-fat coconut milk)
Preheat the oven to 350 F and grease an 8×8 pan or line with parchment paper.
To make the cake, place the flour, baking powder, baking soda, and salt in a large bowl and whisk to combine. Then, add the butter, eggs, vanilla, maple syrup, and milk, and whisk until fully incorporated.
Pour half of the cake batter into the bottom of an 8×8 pan, then sprinkle the 1/3 cup sugar over top, as evenly as possible, followed by the teaspoon of cinnamon. Pour the remaining cake batter over top and spread evenly.
To make the crumble, add the flour, sugar, and cinnamon to a bowl and whisk to combine. Then, stir in the butter until a crumbly mixture forms.
Sprinkle the cinnamon crumble on top of the coffee cake batter, then bake for 40-50 minutes, until a toothpick inserted into the middle of the cake comes out clean.
While the cake is cooling, whisk together the powdered sugar, vanilla, and cream for the icing, then drizzle over top and serve!