Day 1: Prepare Dough and Crumble for Fermentation

Make the Cookie Dough:

• In a large bowl, cream together softened butter, powdered sugar, and brown sugar until light and fluffy (about 2-3 minutes).
• Add egg and vanilla extract, mix well until combined.
• Add sourdough starter and mix until fully incorporated.
• In a separate bowl, whisk together flour, baking powder, salt, and cream of tartar.
• Gradually add dry ingredients to wet ingredients, mixing until just combined. Don’t overmix!
• Dump dough onto plastic wrap, wrap well, and refrigerate for 8-24 hours.

Make the Fermented Crumble (Food Processor Method):

• Add flour, brown sugar, salt, powdered sugar, cinnamon, and sourdough starter to food processor.
• Pulse 3-4 times to combine dry ingredients.
• Add cold cubed butter and pulse 10-15 times in short bursts until mixture resembles coarse crumbs.
• Add vanilla and pulse 1-2 times just to incorporate.
• Continue pulsing until you have a brown sugar-like texture that holds together when squeezed but isn’t a dough ball. Go slowly!
• Cover and refrigerate alongside the cookie dough for 8-24 hours.

Day 2: Assembly and Baking

Prepare the Pecan Pie Filling:

• Optional but recommended: Toast the chopped pecans in a dry medium saucepan over medium heat for 3-5 minutes, stirring frequently, until fragrant and slightly darkened. Transfer to a bowl and set aside.
• In a medium bowl, whisk together melted butter, brown sugar, egg, heavy cream, cornstarch, vanilla extract, salt, and cinnamon (if using) until smooth and well combined.
  
• Fold in the chopped pecans (toasted or untoasted).
• Transfer mixture to a medium saucepan and cook over medium-low heat, stirring constantly, for 5-8 minutes until mixture thickens significantly to a thick custard consistency. The filling should be thick enough that when you drag a spoon through it, it holds its shape and doesn’t immediately flow back together.
• Remove from heat and let cool completely (at least 45 minutes). Cover with plastic wrap pressed directly on the surface and refrigerate until cold. The filling must be completely cool before assembly.

Prepare for Assembly:

• Preheat oven to 350°F (175°C).
• Line a large baking sheet with parchment paper.
• Get your 2.5-3 inch circle cutter or wide mouth canning jar ready.

Assemble the Cookies:

• Using your circle cutter as a guide, spread about 2 rounded tablespoons of fermented crumble mixture on the parchment in circles. Don’t press them together or down. Just loosely arrange in a circle the size of the cutter. Leave small gaps in the crumble for the marbled effect!
  
• Top each crumble circle with 1 rounded tablespoon of cooled pecan pie filling. Gently spread around the middle, keeping it from going over the edges of the crumble.
• Tip: You can take your ball of pecan filling and flatten out into a disk, then place in the middle of the crumble layout.
• Roll out the fermented cookie dough on a floured surface to a rough rectangle, 12” × 10”, approximately 3/8” thick. (The line between 1/4" and 1/2"
• Using your circle cutter, cut out circles from the dough.
• Gently gather scraps, press together to form a ball, and roll out another rectangle. Continue cutting until all dough is used. If the dough resists, wrap and refrigerate for 15-30 minutes.
• Place each cookie circle on top of the crumble and pecan pie layers.
• Gently press down to adhere, making sure the crumble and pecan filling are under the cookie.
• Push any crumble sticking out from under the cookie top back underneath to keep the edges tidy.

Bake:

• Bake for 18-22 minutes, until you can see dark golden browning on the crumble edges around the bottom.
• Remove from oven and let cool completely on the baking sheet for at least 1 hour. Don’t rush this step! The cooling time allows the cornstarch mixture and crumble to set properly.

Add Drizzle (Optional):

• Melt white chocolate with a teaspoon of coconut oil, or warm caramel, until smooth and drizzle-able.
• Using a spoon or piping bag, drizzle over the cooled cookies.