In this modern take on the Eastern European comfort food, leaves of Savoy cabbage turn buttery and tender when braised, and ground turkey replaces the usual beef. It's a colorful entree for fall or winter.
Whisk egg white in a bowl; stir in kasha to evenly coat. Heat a small saucepan over high; add kasha mixture and cook, stirring constantly, until dry and kernels separate, about 2 minutes. Reduce heat to low; stir in boiling water and a pinch of salt. Cover and cook until water evaporates and kasha is tender, about 8 minutes.
With a paring knife, remove core of cabbage. Drop cabbage into a large pot of generously salted boiling water; cook until outer leaves turn bright green and pull easily from head, about 1 minute. Remove outer leaves; transfer to a baking sheet lined with a kitchen towel. Continue boiling cabbage and removing leaves until 12 largest outer leaves are cooked. (Remove remaining cabbage and reserve for another use.) Trim the thick center vein from bottom of each leaf.
Preheat oven to 350 degrees. Heat 3 tablespoons oil in a skillet over medium. Add onion; season with salt and pepper and cook, stirring occasionally, until golden, about 10 minutes. Transfer to a large bowl along with cooked kasha; let cool completely. Whisk remaining egg and stir into kasha mixture with carrots, herbs, turkey, and flour. Season with 1 1/4 teaspoons salt and 1/2 teaspoon pepper.
Line an 8‐inch bowl (measured across top) with a double layer of cheesecloth, leaving about 6 inches of overhang. Then line with the 6 prettiest cabbage leaves, overlapping slightly and allowing them to hang over top of bowl. Layer with one‐third of turkey mixture; top with 2 more cabbage leaves. Repeat layering twice with remaining turkey mixture and leaves. Fold in overhanging leaves to cover filling. Gather cheesecloth overhang and lift cabbage up, twisting to tighten into a secure round.
Place tomatoes and 1 cup water in an ovenproof pot, such as a Dutch oven; bring to a simmer. Season with salt and pepper; stir in remaining 2 tablespoons oil. Place stuffed cabbage, with twisted part of cheesecloth facing down, in pot. Cover, transfer to oven, and roast, basting occasion‐ ally with tomatoes, until a thermometer inserted in center registers 160 degrees, 40 to 50 minutes. Let cool slightly, then remove cheesecloth and slice cabbage into wedges. Serve with pan sauce, sour cream, and herbs.
You can refrigerate boiled and cooled cabbage leaves in an airtight container for up to a day.