In the bowl of an electric mixer, whip cream cheese on medium-high speed for 1-2 minutes or until light and creamy. Add creme fraiche and whip another minute. Scrape bowl regularly, making sure the cream cheese is completely mixed. Add sugar, maple syrup and then eggs, one at a time, ensuring each element is incorporated, one after the next. Add salt, vanilla and lemon zest to finish. Do one final scrape around the bowl after all ingredients are mixed together.