In a small food processor, pulse the spelt flour, dark brown sugar, pecans and butter together until you have a coarse crumble. Set aside in the refrigerator until you are ready to use it.
Make the cinnamon chocolate swirl
In a small bowl, mix the unrefined sugar, cocoa powder and cinnamon together. Set aside.
Make the cake
Preheat the oven to 350°F/176°C. Line an 8-inch x 12-inch pan (23-cm x 33-cm) with parchment paper.
In a large bowl, mix together the spelt flour, baking soda, baking powder and salt.
In a stand mixer fitted with the paddle attachment on medium speed, cream together the butter and sugar for about 5 minutes, until fluffy. Add in the eggs and continue beating for about 1 minute, until they are incorporated. Add in the sour cream and vanilla and continue beating for another 1-2 minutes, until everything is well mixed.
Using a spatula, fold in the flour mixture until everything is just combined, being careful not to over mix.
Carefully pour ⅓ of the cake batter into the prepared pan. Spread it out evenly. Using a spoon, evenly distribute on ½ of the cinnamon chocolate mixture over the cake batter. Carefully pour half of the remaining cake batter on top of the cinnamon chocolate mixture, and spread it out evenly. Using a spoon, evenly distribute the remaining cinnamon chocolate mixture over the cake batter. Carefully pour on the remaining cake batter on top of the second cinnamon chocolate layer. Evenly sprinkle on the crumble topping over the top.
Bake for about about 1 hour, until the cake is golden brown and a toothpick inserted into the middle comes out clean.
To serve, slice the cake into about 4-inch x 1-inch slices (or larger if you prefer). Grill on high heat in a panini press for about 2-3 minutes, until the sides are toasted (or grill both sides on a skillet on medium-high heat). Serve with a slice of salted butter.