Preheat the oven to 375 degrees and line all 12 cups of the muffin tin with liners.

In a separate bowl, combine the 6 tbsp of room temperature butter with the ½ cup of brown sugar, ½ cup of quick oats, and ⅓ cup of flour. Stir together until all the ingredients form crumbles. Set aside for later.

In the mixer, add 1 stick of butter and ⅔ cup of sugar. Mix on medium-high speed with the paddle attachment until sugar and butter are whipped together.

Add in the eggs and mix on medium speed until they are incorporated. You may have to scrape down the sides of the bowl at some point to get the ingredients to thoroughly mix.

Next, add in the teaspoon of vanilla, ½ tsp of salt, 1 ½ tbsp of lemon zest, and 3 tbsp of lemon juice. Mix again to combine. I used the juice from one whole lemon and it came out to be right around 3 tbsp.

After this, add in the ½ cup of sourdough discard*, 1 ¼ cups of milk, 2 cups of blueberries and mix.

Finally, add in the 2 ½ cups of all-purpose flour, 2 tsp of baking powder, and ½ tsp of baking soda, and mix all the ingredients until thoroughly combined and no dry bits of flour can be seen.

Fill a large piping bag (or ziplock bag) with the muffin batter and cut the tip off making a large enough hole for the blueberries to go through. Alternatively, you can simply spoon the batter into each muffin tin.

Fill the muffin tins ¾ of the way full with batter and then sprinkle the oat crumble top evenly over each muffin.

Place on the middle oven rack and bake at 375 for 20-25 minutes, or until the muffins are golden brown. You'll know they are done when you poke through the center of one of the muffins with a toothpick and the toothpick comes out clean.

Remove them from the muffin tin and allow to cool on a cooling rack for 10 minutes, and then enjoy!