Bake the cupcakes. Preheat the oven to 350°F (180°C). Prepare a 12-count muffin pan with paper liners and set aside.
In a medium bowl, combine flour, baking powder, and salt. Whisk to combine and set aside.
1 and 1/2 cups all-purpose flour , 2 teaspoons baking powder, 1/2 teaspoon table salt
Using a handheld or stand mixer fitted with the paddle attachment, beat the butter and sugar together on medium-high speed until creamed, 2-3 minutes.
1/2 cup (1 stick) unsalted butter, 1 cup granulated white sugar
Add eggs and vanilla, scrape down the sides of the bowl, and beat again on medium-high speed until mixture is well-combined.
2 large eggs, 2 teaspoons vanilla extract
Add the dry ingredients to the butter-sugar mixture in three batches, beating on low speed after each addition. Mix in the milk, lemon zest, and juice, and beat again on low speed just until combined. Do not overmix.
1/2 cup whole milk , zest and juice of two medium lemons
Divide batter evenly between 12 cupcake liners, and bake for 18-20 minutes, until a toothpick inserted in the middle of cupcakes comes out clean. Remove from the oven, allow to cool in the pan for 10-15 minutes, then remove to a wire rack to cool completely before filling and frosting.
Fill the cupcakes. Using a small paring knife, cut a small cone out of the center of each cupcake, making a well about 1.5 inches deep. Spoon a small amount of lemon curd into the well. If you like, slice the smooth top edge off of each cone you removed and place it in the hole over the lemon curd filling, so the top of the cupcake still has a smooth surface of cake with the curd underneath. (This is definitely not necessary, but is pretty quick and easy and can make the cupcakes slightly easier to frost.)
1/2 cup lemon curd
Frost the cupcakes. Using a handheld or stand mixer with the paddle attachment, beat the cream cheese and butter on medium-high for 2-3 minutes, until light and fluffy.
8 ounces cream cheese, 5 Tablespoons unsalted butter
Add powdered sugar and mix on low speed just until incorporated, then increase the speed to medium-high and beat 3-4 minutes, until mixture is smooth and light.
2 and 3/4 cups powdered sugar
Add the vanilla and poppy seeds, and beat again 1-2 minutes. Frost cupcakes as desired, serve, and enjoy.
3 teaspoons clear vanilla extract , 1 Tablespoon poppy seeds