Preheat oven to 400 degrees F (200 degrees C).

Line a 12-cup muffin tin with paper liners.

In a large bowl, combine flour, sugar, sour cream, softened butter, egg, poppy seeds, salt, baking soda, orange juice, and orange rind.

Mix at low speed until just moistened, about 1 minute.

Fill muffin liners 1/2 full with batter.

Bake for 17 to 22 minutes, or until a toothpick inserted into the center comes out clean.

While the muffins are baking, prepare the orange cream cheese butter.

In a separate bowl, blend softened butter, cream cheese, powdered sugar, and orange rind until smooth and creamy.

Once the muffins are cooled slightly, top each muffin with the orange cream cheese butter.

Serve immediately or store in an airtight container.