Low-cal Ricotta Cheesecake

• 3 eggs
• 1 egg (white)
• 1 orange peel (grated)
• 425 gr con skim ricotta cheese
• 240 ml buttermilk
• 100 gr granulated sugar
• 45 gr butter
• 30 ml orange juice
• 28 gr packed dark brown sugar
• 14 gr vanilla extract