Line a muffin tin with paper cups, spacing the cups out so they aren't next to each other then grease the outer edge with cooking spray or butter. Set aside.
In a large bowl whisk together to flour, baking powder, baking soda, salt, and allspice.
In another large mixing bowl cream the butter and sugar until light and fluffy. Add the eggs one at a time, scraping the sides if necessary. Add the vanilla and beat until smooth.
Alternately add the flour, greek yogurt, and sour cream to the butter mixture, scraping the sides of the bowl occasionally, and ending with the flour mixture. Don't over mix, the batter should be slightly lumpy. Work in the carrots and toasted walnuts until evenly distributed.
Use an ice cream scooper to fill the muffin cups, piling it up about a 1/2 inch above the rim of the cups.
Bake for 20-25 minutes or until the muffins are golden brown and a toothpick inserted in the center comes out clean.
Meanwhile beat the cream cheese with the paddle attachment for 4 to 5 minutes or until light and fluffy. Add the powdered sugar and milk and beat on medium speed until smooth. Add more milk if you want a thinner consistency.
Drizzle the tops of the muffins with the glaze and enjoy!!