I'm having issues with my lemon cupcakes.  They tend to bake flat or slightly sunken in or they overflow slightly (though that might be from overfilling).  The batter starts to puff up right away.  I tried adding 1/4 tsp of baking soda and slightly whipped the eggs separately (the batter kept looking curdled when I added the eggs) and it didn't help at all.  More overflow and it created a loose irregular crumb.  I'm looking for a tight, even crumb and a slight dome.  Should I adjust the leavener?   Whip the egg whites and incorporate at the end?  Try cake flour?  This the recipe I use:

• 2 1/4 cups AP flour
• 1 tablespoon baking powder
• 1/2 teaspoon salt
• 1 1/4 cups buttermilk (made with whole milk and lemon juice)
• 1 large egg
• 2 egg whites
• 1 1/2 cups sugar
• lemon zest from two lemons
• 1 stick (8 tablespoons) unsalted butter, at room temperature
• 1 teaspoon pure vanilla extract
• 1 teaspoon pure lemon extract

1 tablespoon of baking powder? That's a whole lot of leavening. And with buttermilk you generally want both powder and soda because of the acidity. The overflow and sinking sound like too much leavening. Both of my red velvet and chocolate cake use only 1 teaspoon each of baking soda and baking powder with 1 cup of buttermilk.

This recipe makes about 20 cupcakes.

My lemon uses 2 teaspoons of baking powder and 1/2 teaspoon soda to 2 1/2 cups cake flour, no buttermilk, but I do use sour cream.

I agree with crafty... 1 tablespoon of baking powder is a lot.

Hmmm, most of the recipes in the book Sky High: Irresistible Triple Layer Cakes (which produce really great cake results) use 1 tbsp up to 4 tsps for 8 or 9 inch cakes, so it didn't seem crazy to me.  Maybe that doesn't work as well for cupcakes though.