Step 1

Whisk together spelt flour, rye flour, buckwheat flour, cinnamon, ginger, cardamom, turmeric, white pepper, black pepper, allspice, baking powder, baking soda, cloves, nutmeg, and salt in a medium bowl; set aside.

Step 2

Beat butter, coconut sugar, and granulated sugar in bowl of a stand mixer fitted with the paddle attachment on medium speed until pale and slightly fluffy, about 3 minutes. Add eggs, 1 at a time, beating well after each addition. Add molasses, sourdough starter, and vanilla. Beat until mixture is well combined and resembles ribbons being pulled by the paddle, about 3 minutes, stopping occasionally to scrape down sides of bowl.

Step 3

Reduce mixer speed to low; gradually add flour mixture to butter mixture, beating just until incorporated and smooth, about 1 minute. (Do not overmix. Dough will be thick and soft.) Cover bowl tightly with plastic wrap, and chill at least overnight (12 hours) or up to 5 days. The longer the dough chills, the fluffier and tangier the cookies will be.

Step 4

Remove dough from refrigerator, and let stand, covered, at room temperature until slightly softened, 1 to 2 hours. During final 30 minutes of standing time, preheat oven to 375°F with racks in upper third and lower third positions. Line 4 baking sheets with parchment paper.

Step 5

Stir together granulated sugar and cinnamon in a small bowl; set aside.

Step 6

Using a 2 1/4-inch cookie scoop, divide dough into 2 1/2-ounce portions, leaving 1 side of each scoop flat. Roll the rounded tops and sides of each dough portion in cinnamon-sugar topping. Place dough scoops, flat sides down, at least 2 1/2 inches apart on prepared baking sheets.

Step 7

Bake 2 baking sheets of cookies in preheated oven until cookie edges are set and slightly firm and tops are crackled with dull matte, not glossy, cracks, 14 to 18 minutes, rotating baking sheets between top and bottom racks halfway through bake time. Let cookies cool on baking sheets 10 minutes. Transfer cookies to a wire rack, and let cool completely, about 30 minutes. Repeat baking process with remaining cookies.