Preheat oven to 350 degrees and line 8 cupcake tins with paper cups. In a mixer, cream butter until light and fluffy then add the sugar and mix well. Add the egg and the vanilla then stir. Alternately add the flour and the milk, mixing well after each addition. Add the salt and baking powder then scrape down the sides of the bowl. Add the lemon juice and zest then stir well.
Scoop into cupcake papers filling no more than 3/4 full. Bake for 20-22 minutes or until a toothpick inserted into the centers comes out clean. Remove from oven and allow to cool completely on a wire rack.
For The Strawberry Filling: In a small bowl, mix the strawberries, lemon zest and the sugar and let sit for 10 minutes.
For The Buttercream: In a medium bowl, cream butter until light and fluffy. Add lemon zest then slowly add the powdered sugar til well combined. Mix well then add the lemon juice and beat until fluffy.
To Assemble The Cupcakes: Cut the center of each cupcake out with a sharp paring knife. Spoon strawberry lemon filling into hole then using a large tip, frost over the filling on each cupcake.
NOTE: Makes 8 cupcakes. Recipe can be doubled.