In a medium-sized mixing bowl, beat butter until light and fluffy, about three minutes.
Slowly mix in powdered sugar until fully combined.
Puree raspberries in a food processor or blender. Press through a fine sieve to remove seeds. Measure out 1/4 cup of raspberry puree and mix into the frosting.
Mix in salt and lemon zest.
Spread or pipe on baked goods.
Frosts 12 cupcakes with a medium-sized swirl. Double the frosting recipe if you prefer large frosting swirls.You can leave buttercream out on the counter for up to three days.If you aren't going to be using it right away, store it in an air-tight container and keep it in the refrigerator for up to a week or in the freezer for up to a month. Bring frozen frosting back to room temperature by first putting it in the refrigerator overnight and then leaving it on the counter for a few hours. You will also need to re-whip it before use.