In a large bowl, place the Peeled & cubed potato and chopped carrots. In a smaller bowl, put the minced garlic, chopped scallions & celery.
In a large saucepan, warm 3 tablespoons of butter over medium-high heat until it is melted. Add the garlic-scallion-celery mixture and saute, stirring until the scallions are wilted, about 2 minutes.
Stir in flour and cook, until the flour is no longer visible, about 1 minute. Slowly pour in the chicken broth, stirring constantly. Bring the mixture to a boil and then add the potato, carrots, pepper and 1/4 tsp. nutmeg. Let mixture return to a boil, then reduce the heat to medium-low, cover and simmer until the potatoes are tender, about 15 minutes.
Meanwhile, drain the crabmeat and pick out any pieces of shell or cartilage. Toast thr bread.
In a small saucepan or skillet, combine the remaining 4 tsp. butter with the remaining 1/2 tsp. nutmeg and cook over low heat until fragrant, about 1 minute. Brush the toast with the nutmeg butter and cut into triangles.
Increase the heat under the soup to medium-high and bring to a boil. Add the crab, and milk, and cook until just heated through, about 3 minutes. Serve the soup with the nutmeg croutons.