Preheat the oven to 350 degrees 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.
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. Add the eggs and vanilla, scrape down the sides of the bowl, and beat again on medium-high speed until mixture is well-combined.
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!
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.
To fill the cupcakes, use a small paring knife to cut a small cone out of the center of each cupcake, making a well about 1-1 1/2 inches deep. Spoon a small amount of lemon curd into the well. If you like, you can slice each cone you removed and replace just the top edge, 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.)
To make the frosting, slice green tops from the strawberries, then puree in a food processor or blender until smooth. Strain puree through a wire sieve to remove seeds; you should have about 3/4 cup of puree.
Transfer puree to a small saucepan over medium heat and bring to a boil. Allow the mixture to boil gently for 15-20 minutes, until the mixture has reduced to about 1/4 cup. Remove from the heat and place mixture in the fridge to cool.
Using a handheld or stand mixer fitted with the paddle attachment, beat butter on medium-high speed until fluffy, then beat in 1 1/2 cups of the powdered sugar. Turn mixer down to low and beat in 2-3 tablespoons of the chilled, reduced strawberry puree. Add the rest of the powdered sugar and beat on medium-high speed until frosting is thick and creamy.
Frost cupcakes as desired - I used a Wilton 1M tip. Enjoy!