Preheat oven to 350°F (180ºC). In large bowl, whisk together flour, baking powder, baking soda and salt. Set aside. In food processor or blender, process beets, buttermilk, cocoa powder and vanilla into a puree. Set aside.
In bowl, with hand-mixer, beat butter until soft then beat in sugar until fluffy. Beat in eggs, one at a time, incorporating each one before adding next. With mixer on low, alternately beat in dry mixture in 3 parts with wet mixture in 2 parts, starting and ending with dry. Scrape bowl as needed between additions. Scrape batter into greased and floured 9 x 5-in. (1.9 L) loaf pan, smoothing top.
Bake 45 to 50 min., or until a cake tester comes out clean when inserted into centre. Cool cake completely in pan on wire rack.
Meanwhile, drain ricotta in cheesecloth lined fine mesh sieve. Squeeze to remove excess moisture. Transfer ricotta to (clean) food processor and pulse until smooth. Add butter; pulse until light and fluffy. Add icing sugar and vanilla; pulse until smooth (if icing is too soft to spread, refrigerate 10 to 15 min. to firm up). Spread icing over top of cooled loaf. Refrigerate 2 hr. or until icing is firm. Store chilled in airtight container up to 2 days.
Garnish iced cake with raspberries.