In a large bowl, whisk together the flour, cinnamon, baking powder, and salt. In another bowl, beat the eggs and then mix in the milk, melted butter, and sugars. Combine the wet and dry ingredients until just mixed. Preheat a waffle iron and pour the batter in, cooking according to the manufacturer's instructions until crispy and golden brown.

Make the Streusel

In a medium bowl, mix together the chopped walnuts, brown sugar, and a pinch of cinnamon. Sprinkle this mixture over the waffles before serving.

Whip the Cream

In a mixing bowl, combine heavy cream and powdered sugar. Using an electric mixer, whip until soft peaks form.

Prepare the Blackberry Coulis

In a small saucepan, cook the blackberries over medium heat until they break down, about 5-7 minutes. Mash them gently with a fork and strain through a fine mesh sieve to remove the seeds. Set aside.

Serve

To assemble, stack two waffles on a plate, drizzle with warm dulce de leche, add a dollop of whipped cream, and drizzle the blackberry coulis on top. Sprinkle with cinnamon streusel and serve immediately.