Crust
Step 1
Whisk 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, ¼ tsp. baking powder, and 1⅔ cups (208 g) all-purpose flour in a large bowl. Add 2 oz. chilled cream cheese, cut into 1″ pieces, and rub in with your fingers until incorporated (mixture will look very shaggy). Add 10 Tbsp. chilled unsalted butter, sliced ½” thick, and toss to coat in flour, then smash into smaller, flatter pieces (about chickpea size). Make a well in the center and pour in ¼ cup ice water. Toss with a fork or your hands to distribute. Knead dough in bowl just to bring together (some dry bits may remain).
Step 2
Turn dough out onto a lightly dusted surface and sprinkle with all-purpose flour. Roll out to a ½”-thick rectangle. Fold in half, rotate 90°, and fold in half again. Roll out again to a ½”-thick rectangle and repeat folding process, dusting dough with more flour as needed to prevent sticking. Pat into a ½”-thick disk and wrap tightly in plastic. Chill at least 2 hours and, preferably, up to 12 hours.
Do Ahead: Dough can be made 1 month ahead. Wrap disk in 2 layers of plastic and freeze instead of chilling. Thaw in refrigerator 12 hours before using.
Filling and Assembly
Step 3
When dough is almost done chilling, cut 1 medium head of savoy cabbage (1¾–2¼ lb.) in half and cut out triangular core at bottom; discard. Separate leaves and tear into pieces about the size of your palm. Transfer about half to a large bowl and set aside.
Step 4
Melt 1 Tbsp. unsalted butter in a large skillet over medium heat. Add 1 medium white or yellow onion, thinly sliced, and season generously with kosher salt. Cook, stirring occasionally, until softened and starting to turn translucent, about 5 minutes. Add remaining 1 Tbsp. unsalted butter and ¾ tsp. cumin seeds (if using) and cook until butter is melted. Add remaining cabbage leaves and cook, stirring occasionally, until onion is translucent and lightly browned and cabbage is wilted, 18–22 minutes. Transfer to a large plate or a small baking sheet; chill in fridge or freezer until cool.
Step 5
Place a rack in bottom third of oven; preheat to 400°. Whisk 2 garlic cloves, finely grated, ⅓ cup heavy cream, 2 Tbsp. Dijon mustard, and ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt in a measuring glass to combine. Pour cream mixture over reserved raw cabbage leaves and toss with your hands to coat. Add 5 oz. Gruyère or sharp cheddar, coarsely grated, and toss again to combine.
Step 6
Unwrap dough and roll out on a lightly floured sheet of parchment paper to a 13–14″ round (some dough will extend beyond the parchment). Transfer on parchment paper to a baking sheet.
Step 7
Spread cooked cabbage mixture over dough, leaving about a 1½” border
around edges. Fold dough up and over filling, folding and tucking as needed to make a
rustic border. Pile raw cabbage mixture on top of cooked cabbage mixture to make a
dramatic heap. (It will look ridiculously high at first but will cook down when it
bakes.)
Step 8
Bake galette 25 minutes. Rotate baking sheet front to back, reduce heat to 375°, and bake until cabbage and crust are deep golden brown, 25–35 minutes. (If cabbage seems to be browning too much, reduce heat to 350° toward the end.) Let galette cool on baking sheet at least 1 hour and up to 4 hours before serving.
Do Ahead: Sautéed cabbage can be made 1 day ahead. Transfer to an airtight container and chill. Tightly wrap undressed raw cabbage in plastic and chill.
