Wash beet leaves. Pat leaves dry and set aside.
Dissolve yeast in warm water in a large bowl; let stand 5 minutes. Stir in buttermilk and 1/2 teaspoon salt. Lightly spoon flours into dry measuring cups; level with a knife. Add 1 cup bread flour and all-purpose flour to buttermilk mixture; stir to form a soft dough. Turn the dough out onto a lightly floured surface. Knead until smooth and elastic (about 8 minutes); add enough of the remaining bread flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel tacky).
Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in size. (Gently press two fingers into dough. If indentation remains, dough has risen enough.) Punch dough down; cover and let rest 5 minutes.
Roll dough into a 12 x 4-inch rectangle on a lightly floured surface. Cut rectangle crosswise into 12 (1-inch) strips. Working with 1 portion at a time (cover remaining dough to prevent drying), wrap a leaf around middle of each dough strip, starting with the stem end. (Ends of breadsticks should not be covered by leaf.) Place breadsticks, leaf tips down, on a baking sheet covered with parchment paper. Brush the breadsticks with melted butter; sprinkle with kosher salt. Cover and let rise 45 minutes or until doubled in size.
Preheat oven to 375°.
Bake breadsticks at 375° for 35 minutes or until browned on bottom and lightly browned on top. Remove from pan; cool on a wire rack. Serve with the sour cream, if desired.