The night before, make the sponge. In a large mixing bowl combine the sourdough discard, buttermilk, flour, sugar, and melted butter until fully mixed. Cover with a clean kitchen towel and allow to rest at cool room temperature (about 65 - 70 degrees F) overnight, about 8-12 hours.

The following morning, just before you want to cook the pancakes, add the egg, vanilla, salt, baking powder, and baking soda, stirring until just combined. It's important that the baking powder and baking soda go in just before cooking for the fluffiest pancakes.

If leaving your buttermilk sponge out overnight makes you uncomfortable for food safety reasons or if your kitchen is especially warm, you can certainly assemble the pancake batter the same morning you plan to cook the pancakes. To maximize fluffiness, you can allow the sponge (sourdough discard, buttermilk, flour, butter) to rest for up to two hours at a cool room temperature before adding the remaining ingredients (egg, vanilla, salt, baking powder, baking soda). For lighter, less fluffy sourdough pancakes, you can skip the resting time and make the batter right before you plan to cook the pancakes. For either option, make sure that the leavening agents (baking soda and baking powder) are added in just before you plan to cook the batter so it doesn't fall flat.

Preheat a cast-iron or non-stick skillet over medium-high heat. Add a small amount of butter or canola oil to the pan to lightly coat. Once the pan is hot, pour pancakes in ½ cup increments into the pan, taking care not to crowd the pancakes or they'll spread together. Cook until bubbles form at the top and sides of the pancake and the underside is golden (about 2-3 minutes), then flip and cook the opposite side until golden (about 2 minutes). Repeat with the remaining batter in ½ cup increments per pancake. You should get 7-8 pancakes depending on how far down the batter has been stirred. Reserve pancakes to the side on a plate with a clean towel on top to help retain their heat.

In a medium saucepan over medium heat, combine the frozen blueberries, maple syrup, lemon juice, vanilla, cinnamon, and cardamom. Allow to cook down, stirring occasionally until syrupy and soft. The juices from the blueberries will thicken as the mixture cooks. If you'd prefer to thin the syrup down, you can add water in 1 tbsp increments until it reaches your desired consistency. Serve warm over top of the pancakes with optional whipped cream on top.