Prep: Preheat oven to 425°F. Spray a 12-cup muffin tin (and/or liners) with nonstick spray.
Infuse the sugar: In a large bowl, zest the lemons directly into the sugar. Use your fingers to rub the zest into the sugar until fragrant and yellow.
Add wet ingredients: Stir in the lemon juice, eggs, and Greek yogurt until smooth. Fold in the poppy seeds.
Add fats: Melt the butter, then stir in the oil to cool it down. Add to the bowl and mix well.
Add dry ingredients: Sprinkle flour, baking powder, baking soda, and salt over the top. Gently fold everything together just until no dry streaks remain.
Rest the batter: Let the batter sit for 15 minutes. This helps hydrate the flour and poppy seeds.
Scoop: Divide the batter evenly between the 12 muffin wells.
Add lemon curd filling (optional): If filling with curd, spray or wet the back of a tablespoon and press into the center of each muffin to make a well. Spoon in a heaping tablespoon of lemon curd.
Bake: Bake at 425°F for 5 minutes. Without opening the oven, reduce the temp to 350°F and bake for 15–18 more minutes, or until a toothpick comes out clean or muffins reach 190°F internally.
Cool: Let muffins cool in the pan for 5 minutes, then transfer to a wire rack.
Glaze: Whisk together powdered sugar, lemon juice, and cream until smooth. Dip warm muffin tops into the glaze and swirl gently. Let set on the rack until cooled and set.