Preheat oven to 350°F (175°C). Grease and flour a standard 9x5 inch loaf pan.

Prepare the filling: In a medium bowl, toss the chopped rhubarb with 1/4 cup sugar and 1 tablespoon of flour until evenly coated. Set aside.

Make the streusel: In a small bowl, combine the 1/2 cup flour, brown sugar, and cinnamon. Cut in the cold butter using a pastry blender or your fingers until coarse crumbs form. Refrigerate until ready to use.

Prepare the batter: Whisk together the 1 3/4 cups flour, baking soda, and salt in one bowl. In a separate large bowl, cream together the 1 cup sugar and 1/2 cup softened butter until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract.

Alternate adding the dry ingredients and buttermilk to the wet mixture, beginning and ending with the dry ingredients. Mix only until just combined; do not overmix.

Gently fold the prepared rhubarb mixture into the batter. Pour the batter into the prepared loaf pan.

Sprinkle the chilled streusel topping evenly over the top of the batter. Bake for 50-55 minutes, or until a wooden skewer inserted near the center comes out clean. If the top browns too quickly, loosely tent with foil after 40 minutes.

Let the bread cool in the pan for 15 minutes before inverting it onto a wire rack to cool completely. Slice thickly and serve.