First, preheat the oven to 350° Fahrenheit and line your cupcake pans with cupcake paper liners. Then, make your cupcake batter! In a large bowl, cream together the room temp butter and white sugar. Then add in one egg at a time, beating together in between additions. Finally, puree the chopped strawberries together with the milk, using a blender or food processor, then add the puree into your batter and whisk to combine. Whisk in the vanilla until smooth. Whisk in the flour (and xanthan gum if needed), then add the baking powder and soda, and salt and whisk until smooth.
Then scoop the batter into cupcake pans and bake for 18-22 minutes or until a skewer into the center of the cupcakes comes out clean. Let cupcakes cool completely before filling and frosting.
While the cupcakes are cooling, make your filling and frosting! First, finely chop your strawberries, mix with the lemon juice and sugar and set aside to macerate. Then make the frosting! In a large bowl, using an electric mixer, beat the room temp butter for 1-2 minutes until lighter, then add in the cream cheese and one cup of the powdered sugar, and the vanilla extract and beat until smooth. Continue adding powdered sugar until you've reached your desired sweetness and thickness, then scoop frosting into a piping bag with your choice of piping tip.
Finally, using a spoon or a paring knife, cut out a 1-inch hole in each cupcake (save the piece you cut out), spoon in about a teaspoon of the finely chopped strawberries, then put the cut out piece back on top and press in. Then pipe frosting on top, and serve!