Whisk sugar, cinnamon, and butter in medium bowl to combine.

Add flour and stir until mixture resembles thick, cohesive dough.

Set aside to cool to room temperature for 10 to 15 minutes.

Preheat the oven to 325 degrees Fahrenheit.

Spray mini loaf pans with nonstick cooking spray. You can also use an 8×8 square pan and line it with Gefen Parchment Paper for easier cake removal.

In bowl of standing mixer fitted with a paddle attachment, mix flour, sugar, baking soda, and salt on low speed to combine.

With mixer running at low speed, add margarine one piece at a time. Continue beating until mixture resembles moist crumbs.

Add egg, yolk, vanilla, and buttermilk; beat on medium- high speed until light and fluffy for about one minute.

Transfer batter to your pan of choice and using a spatula, spread batter into an even layer.

Break apart crumb mixture into big chunks and spread generously over batter, beginning with edges and then working towards the center.

Bake until the crumbs are golden and a toothpick inserted into the center of the cake comes out clean, about 55 minutes.

Dust with confectioners’ sugar just before serving.