Heat oven to 350 degrees F. Add cupcake liners to the pan and set aside.
In a bowl, combine flour, baking powder and salt.
In another large mixing bowl cream together the butter and sugar on medium - high speed for 1 minute. Pause to scrape the bowl, add in the eggs, vanilla and lemon juice/zest. Mix again just to combine.
On low speed add in half the buttermilk and half the flour mixture alternating until fully combined.
Using a 1 inch cookie scoop add 3 Tbsp of batter into each cupcake liner and bake for 20 minutes or until a toothpick inserted into the middle comes out clean.
To make the frosting add raspberries to a blender or food processor. If needed, add a small amount of water to help the raspberries to blend.
Put the raspberries through a sieve to remove the seeds. Add the remaining liquid into a saucepan and bring to a low boil for 10 minutes. Stirring occasionally. The raspberry liquid should reduce greatly and thicken.
Place the raspberries in the freezer to chill for at least 10 minutes.*
Meanwhile, in a large bowl mix the butter on medium high for 1 minute. Slowly add in the powdered sugar. Pause the scrape the sides, add in the heavy cream and salt if desired. Mix again for another minute.
Add 2 Tbsp of raspberry mixture to the frosting and mix until frosting is light and fluffy.
Transfer frosting to a piping bag and pipe on cooled cupcakes.
*Raspberry mixture MUST be fully cooled before adding into the frosting.