Step 1

In a large bowl, cut 1 cup butter into flour until crumbly, leaving pea-sized chunks. Stir in sour cream, and mix well; dough will be very sticky. Form dough into a ball. Cover tightly, and refrigerate 8 hours, or overnight.

Step 2

Preheat oven to 375 degrees F (190 degrees C). Lightly grease a baking sheet. Prepare the filling by combining 1 cup butter, brown sugar, and 1 cup chopped walnuts.

Step 3

Divide dough into three equal parts; return two parts to the refrigerator to keep cold. Quickly form 1/3 of the dough into a rectangle, and flour lightly. On a heavily floured surface, roll out to approximately 12x17 inches. Position lengthwise on the work surface. Along the long edges of the dough rectangle, use a sharp knife to cut 4 inch long angled lines about 1/2 inch apart. Spoon 1/3 of the filling along the length of the rectangle's uncut center. Alternating from one side of the dough to the other, fold each 1/2 inch wide strip towards the center, crisscrossing the filling in a braid-like fashion. Lightly press together the ends of the strips to seal. Sprinkle with 1/3 of the remaining walnuts. Repeat with remaining ingredients to form 3 braided danishes. Arrange danishes on prepared baking sheet.

Step 4

Bake for 30 minutes in the preheated oven, or until golden brown. Cool for approximately 30 minutes. While the danishes are cooling, prepare the icing: mix confectioners sugar and water until smooth. Drizzle in fine streams over warm danishes.