Preheat oven to 350°F. Line a 12-cup muffin pan with paper cases.
Beat the marzipan, eggs, and butter with a wooden spoon until smooth. Gradually mix in the buttermilk, sugar, orange zest, and liqueur with a wooden spoon until light and fluffy.
Sift flour and baking powder into a large bowl. Add marzipan mixture; stir until just combined.
Peel the orange, removing the white pith. Segment the orange and cut the segments in half.
Place 1 teaspoon of mixture in each muffin cup and place a halved orange segment on top. Add more mixture until cups are two-thirds full. Sprinkle with flaked almonds.
Bake for about 20 minutes until golden brown. Place pans on a wire rack; let muffins cool completely.