In a large bowl, cream together softened butter, powdered sugar, and brown sugar until light and fluffy (about 2-3 minutes).

Add egg, vanilla extract, and almond extract (if using). 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. Do not overmix.

Wrap dough tightly in plastic wrap and refrigerate for 12-24 hours.

In a medium bowl, mix together flour, brown sugar, salt, powdered sugar, and sourdough starter.

Add cold cubed butter and cut in using a pastry cutter or your fingers until mixture resembles coarse crumbs.

Add vanilla and mix gently until just incorporated.

Cover bowl and refrigerate alongside the cookie dough for 12-24 hours.

Add flour, brown sugar, salt, powdered sugar, 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.

Transfer to a bowl, cover, and refrigerate alongside the cookie dough for 12-24 hours.

In a medium saucepan, combine blueberries, granulated sugar, cornstarch, lemon juice, and lemon zest (if using).

Cook over medium heat, stirring gently, for 8-10 minutes until blueberries begin to burst and release their juices.

Continue cooking for 2-3 more minutes until mixture thickens and becomes glossy.

Most blueberries should burst but some can remain whole for texture. Remove from heat.

Let cool completely for at least 30 minutes. The compote will thicken considerably as it cools.

Preheat oven to 350°F (175°C).

Line a large baking sheet with parchment paper.

Prepare your 2.5-3 inch circle cutter (or use a wide mouth canning jar).

Top each crumble circle with 2 teaspoons of cooled blueberry compote. Gently spread to cover the crumble.

Roll out the fermented cookie dough on a well-floured surface to a rough rectangle, approximately 13”x 12”, about 3/8” inch thick.

Using your circle cutter, cut out circles from the dough.

Gently gather scraps, press together to form another rectangle, and continue cutting until all dough is used.

Place each cookie circle on top of the crumble and blueberry layers.

Gently press down to adhere, making sure the crumble and blueberry compote are underneath the cookie.

Bake for 18-20 minutes, until cookie tops are golden brown and set. You should see browning on the bottom edges.

Remove from oven and let cool COMPLETELY on the baking sheet (at least 1 hour). This is crucial for the compote to set properly.

Melt white chocolate with 1-2 teaspoons coconut oil in a microwave (stirring every 20 seconds) or in a double boiler until smooth.

Using a spoon or piping bag, drizzle melted white chocolate over the completely cooled cookies.

Let chocolate set for about 1 hour before serving.

Serve immediately or store covered at room temperature for up to 2 days.

Refrigerate after 2 days for up to 5 days total.