Preheat oven to 425 degrees.
Line a muffin tin with muffin liners and set aside.
In a medium sized mixing bowl add the sugar and oil, using a whisk, spatula, or wooden spoon, stir to fully combine.
1 cup granulated sugar, 1/2 cup vegetable oil
Add the eggs one at a time to the sugar-oil mixture making sure they're fully incorporated.
2 medium eggs
Once the eggs are fully incorporated add the vanilla extract, applesauce, and sourdough discard, stir to combine all of the ingredients together. Set aside.
1 tsp vanilla extract, 3/4 cup applesauce, 1/2 cup sourdough discard
In a separate bowl add the all-purpose flour, salt, baking powder, baking soda, cinnamon, ground cloves, and freshly ground nutmeg. Stir to combine.
1 cup all purpose flour, 1 1/2 tsp salt, 1 1/2 tsp baking powder, 3/4 cup baking soda, 1 tsp cinnamon, 1/2 tsp clove, 1/8 tsp freshly ground nutmeg
Add the dry ingredients to the wet ingredients. Gently fold the dry ingredients into the wet ingredients avoiding to over mix the batter. Set aside.
In a small mixing bowl add the all-purpose flour, granulated sugar, salt, cinnamon, freshly ground nutmeg, unsalted butter, and sourdough discard. Using a fork or pastry cutter, cut the wet ingredients into the dry ingredients until it resembles a crumb texture.
1/2 cup all purpose flour, 1/3 cup granulated sugar, 1/4 tsp salt, 1/4 tsp cinnamon, 1/8 tsp freshly ground nutmeg, 2 tbsp unsalted butter, 2 tbsp sourdough discard
Add the walnuts to the mixture and stir to combine so the walnuts are evenly distributed. Set aside.
1/4 cup walnuts,
Fill the muffin tins with the muffin batter so they're 3/4 full in each muffin space. Top with the streusel topping.
Bake muffins at 425 degrees for 10 minutes.
After 10 minutes reduce the heat to 350 degrees and bake for an additional 15-20 minutes or until the tops are golden brown and when a toothpick is inserted into the center of the muffin the toothpick comes out clean.
Transfer the baked muffins to a cooling rack and allow to cool for 5 minutes before eating.