Prizewinning Lemon Blueberry Muffins

• 1 egg
• 1 lemon extract
• 1/2 stick
• 250 gr unsifted all-purpose flour
• 220 ml container low fat yogurt (plain)
• 130 gr sugar
• 5 gr baking powder
• 5 gr baking soda
• 4 gr lemon rind (grated)
• 4 gr vanilla extract