Zest 1-2 lemons (2 tbsp) and mix with 1 cup of granulated sugar. Incorporate the zest into the sugar with your fingers. This will help flavor the muffins evenly.
Mix dry ingredients in a large bowl - flour, sugar, baking soda, salt, and poppy seeds
Whisk together wet ingredients in a medium bowl - melted butter, sourdough discard, oil, sour cream, vanilla, lemon juice, and milk
Gently fold in the wet ingredients into the dry until just combined.
Let batter rest for 30 - 60 minutes before baking.
Preheat the oven to 400 degrees F and prep muffin tins with a liner of choice.
Gently scoop batter into muffin tins using a 2 oz ice cream scoop or a 1/4 cup measuring cup
Optional: Top is course sugar for a bakery-style topping
Bake at 400 for 10 minutes. After 10 minutes, reduce oven temp to 350 degrees and continue cooking for 8-10 more minutes until they are lightly golden on top
Let cool in muffin tin for a few minutes before moving to a cooling rack.