In a separate bowl, whisk together the melted butter, vegetable oil, eggs, sour cream, vanilla extract, lemon zest, lemon juice, and milk until smooth.

Pour the wet ingredients into the dry ingredients and gently fold everything together using a rubber spatula. Mix only until no dry streaks remain. Avoid overmixing, as this can make the muffins dense.

Cover the bowl with plastic wrap and let the batter rest at room temperature for 1 hour. This resting period helps hydrate the flour and creates taller, fluffier muffins.

While the batter rests, prepare the lemon simple syrup. In a small saucepan, combine the lemon juice and sugar. Bring the mixture to a gentle boil over medium heat, then reduce to a simmer for about 5 minutes until the sugar dissolves completely.

Place the lemon zest into a heatproof bowl and pour the hot syrup over it. Allow the syrup to cool while the batter finishes resting.

Near the end of the resting time, preheat the oven to 425°F (220°C). Line a standard muffin pan with 11 paper liners.

Using a large cookie scoop or about ¼ cup of batter, fill each muffin liner completely full, slightly mounding the batter above the rim for tall bakery-style tops.

Bake at 425°F for 8 minutes. Without opening the oven door, reduce the temperature to 350°F (175°C) and continue baking for another 8 to 10 minutes, or until a toothpick inserted into the center comes out clean with only a few moist crumbs.

Remove the muffins from the oven and immediately brush the tops generously with the warm lemon simple syrup.

Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack. Sprinkle with additional poppy seeds or a little extra lemon zest if desired, then enjoy warm or at room temperature.