1. Mix 2 cups flour, sugar, salt and undissolved yeast in a large mixing bowl.
2. Combine sour cream, water and butter; heat to between 120° to 130°F. (Note: butter may not melt completely). Gradually add to dry ingredients and beat for 2 minutes at medium speed of electric mixer.
3. Add eggs and 1 cup flour. Stir in enough remaining flour to make a soft dough. Turn out onto lightly floured surface; knead 8 to 10 minutes to form a ball.
4. Cover and let dough rest 10 minutes.
5. For filling, melt butter over low heat. Stir in sugar and maple flavoring. Add walnuts; blend well. Set aside.
6. Divide dough into 4 equal pieces. Roll out each piece into a 14 x 12-inch rectangle. Spread each with an equal amount of nut filling. Roll each up from the long side; seal edges. Place on greased baking sheets; sealed edges down. Cover. Let rise in a warm, draft free place until doubled in bulk, about 1 hour.
7. For frosting, combine sugar, milk and vanilla until mixture reaches desired consistency. Drizzle over each roll.

Variation: To make Pecan Nut Rolls, use the following filling. Melt 1 cup butter over low heat. Stir in 1/2 cup sugar and 3 tablespoons vanilla extract. Add 7 cups ground pecans; blend well.