We haven't baked this recipe since late summer, so naturally, when I pulled it out of the 'archives', I decided to perfect the icing and the consistency. Much to my delight, it is more moist and flavorful. It's my new favorite.
(I prefer to use pure extract, and Watkins from Walmart affords me that opportunity without losing profitability).
After mixing your wet ingredients (because I like them to reach room temperature before making the batter), sift/whisk dry ingredients & grate as much orange peel into your dry mixture as you desire.The recipe just gives a guideline. 
JUST combine wet into dry ingredients and fold in 1/2 cup of almonds. (Reserve remainder for topping). Bake and cool the muffins completely before adding icing and almonds.
For the icing, add melted butter to confectioner's sugar. Then, add orange juice & vanilla & whisk.
Add a tablespoon of milk at a time, using only what you need to reach desired consistency. Grate more orange peel into the icing (as much or as little as you desire) and stir.
Once muffins are cooled, top with icing and sliced almonds!
ORANGE ALMOND MUFFINS
INGREDIENTS:
2 C flour
2 T baking powder
1/2 tsp salt
3.4 C sugar
1 lg egg
1 C milk
1/3 C veg oil
1 T orange zest
1 tsp orange extract
2/3 C sliced almonds
Icing:
1+ T milk
1 C confectioner's sugar
1/2 stick (1/4 C) butter, melted
1/8 tsp vanilla (to taste)
1/2+ T orange juice
1 T orange zest
INSTRUCTIONS
Preheat oven to 375F. Line jumbo muffin tins with paper liners. In medium bowl, whisk together egg, milk, oil, orange extract. In large bowl, whisk together flour, baking powder, salt, and sugar. Stir orange zest into flour mixture to coat. JUST combine wet mixture into dry ingredients and fold in 1/2 cup almonds. Fill muffin cups 2/3 full. Bake 20-25 minutes. Cool completely! Icing: add melted butter to confectioner's sugar. Stir. Add vanilla and orange juice to mixture and whisk well. Add milk, one tablespoon at a time in order to reach desired consistency. Stir in orange zest.
Top cooled muffins with icing and remaining almond slices.
