In a mixer fitted with the paddle attachment, beat together butter and sugar on medium speed for 3-4 minutes until light and fluffy. Scrape down the sides and bottom of the bowl occasionally. Add eggs, one at a time, beating well after each addition. Beat in vanilla extract and lemon zest, if using. On low speed, beat in flour mixture in 3 additions, alternating with the buttermilk/sour cream in 2 additions, starting and ending with the flour. Do not overmix. Fold in raspberries and white chocolate.