Preheat your oven to 350°F (175°C). Grease a 9-inch baking pan or a 9-inch springform pan. If using a springform pan, place it on a parchment-lined baking sheet to catch any potential drips. (A springform pan makes it easy to remove the cake while keeping the sides intact for a beautiful presentation.)
In a large bowl, whisk together the all-purpose Spelt flour, whole-grain Spelt flour, unrefined whole cane sugar (Sucanat), baking powder, and salt.
In a separate bowl, mix the milk, melted butter, egg, and vanilla extract until combined.
Add the wet ingredients to the dry ingredients and stir gently until just combined. A key tip here is to avoid over mixing, especially with spelt, to keep the cake tender and soft!
Pour the batter into the prepared pan, spread it out evenly, and smooth the top.
Place the filled pan into the oven and bake for approximately 20 minutes.
While the cake is baking, prepare the topping. In a small bowl, mix the Sucanat, brown sugar, and cinnamon. With clean hands, work the butter into this mixture until it appears crumbly like wet sand with bits of pieces of butter throughout. (See video.)
After the cake has baked for 20 minutes, open the oven door and carefully sprinkle the topping on top of the batter. This will create a perfectly golden top and eliminate any chance of burning.
Continue baking the cake for an additional 15-20 minutes (for a total of 35-40 minutes) or until a toothpick inserted into the center comes out clean.
Once the coffee cake is finished baking, turn off the oven and transfer the pan to a cooling rack.
If using a springform pan, carefully release the sides after about 10 minutes of cooling.
If desired, dust the coffee cake with one teaspoon of confectioner's sugar (icing sugar).
Enjoy this cake warm or at room temperature.