Preheat your oven to 350°F (175°C). Wash and trim approximately 2 cups of fresh rhubarb stalks, chopping them into bite-sized pieces.

In a medium bowl, combine ½ cup of granulated sugar, ½ cup of all-purpose flour, 1 teaspoon of ground cinnamon, and ½ cup of cold butter, diced into small cubes. Mix until the mixture resembles coarse crumbs.

In a large mixing bowl, whisk together 2 large eggs and 1 cup of granulated sugar until fluffy and pale. Gradually blend in ½ cup of melted butter, 1 teaspoon of vanilla extract, and ½ cup of sour cream until fully incorporated.

In a separate bowl, whisk together 1.5 cups of all-purpose flour, 1 teaspoon of baking powder, and ½ teaspoon of baking soda. Gradually add this dry mixture to the wet ingredients, stirring gently until just combined.

Grease a 9-inch square pan. Pour half of the coffee cake batter into the pan, layer with half of the chopped rhubarb, then add remaining batter on top and finish with the rest of the rhubarb and streusel topping.

Bake for 45-50 minutes or until a toothpick comes out clean. The top should be golden-brown.

Let the cake cool in the pan for about 15 minutes before serving. Optionally dust with powdered sugar before slicing.