1-1/4 cups cake flour - (161 grams)
1/2 +1/8 teaspoon baking powder - (3.4 grams)
1/2 teaspoon kosher salt - (1.7 grams)
1 cup + 3 tablespoons granulated sugar - (234 grams)
1/2 cup + 3 tablespoons eggs - (170 grams) [about 3 extra large eggs]
3/4 teaspoon vanilla paste - (4.5 grams)
6.8 ounces unsalted butter, melted and still warm - (194 grams) [about 10 Tbsp.]
1/4 cup fresh lemon juice - (60 grams)
1 tablespoon (generous) grated lemon zest - (6 grams)
1-1/2 teaspoons poppy seeds - (4 grams)
For the Batter:
Sift the cake flour and baking powder into a medium bowl. Add the salt and whisk to combine.
Combine the sugar, eggs, and vanilla paste in a deep medium bowl and mix with an immersion blender. Add the dry ingredients in 2 additions, mixing until just combined. With the blender running, pour in the butter in a steady stream, and continue to mix until the batter is smooth. Add the lemon juice and blend again to combine.
Fold in the lemon zest and poppy seeds (see Note). Transfer the batter to a covered container and refrigerate overnight, or for up to 36 hours.
To Bake the Muffins:
Preheat the oven to 425°F (standard). Line the muffin pan with the muffin papers and spray the papers with nonstick spray.
Transfer the batter to the pastry bag, or use a large spoon, and pipe or spoon the batter evenly into the papers, stopping 3/8-inch from the top (135 grams each for jumbo; 67 grams for standard).
Place the pan in the oven, lower the oven temperature to 325°F, and bake 34 to 37 minutes, [20 to 25 minutes for standard size muffins], or until the muffins are golden brown and a skewer inserted in the center comes out clean. Set the pan on a cooling rack and cool completely.
The muffins are best the day they are baked, but they can be wrapped individually in a few layers of plastic wrap or stored in a single layer in a covered container at room temperature for up to 3 days or frozen for up to 1 week.
Optional light lemon glaze: Mix 1 cup of powdered sugar with 1-2 tablespoons fresh lemon juice. Add just enough juice so that the icing ribbons disappear within 5 seconds.]