Melt butter in a saucepan over medium heat. Add garlic and celery; cook and stir until softened, 4 to 5 minutes. Pour in chicken broth, increase heat to medium-high, and bring to a simmer. Stir in almond butter until dissolved and season with mace. Reduce heat to medium-low, cover, and simmer until the celery is tender, 30 to 40 minutes.

Once the celery is tender, turn off heat, and allow the soup to stand covered for 1 hour.

Carefully puree the warm soup until smooth using a blender or immersion blender; pour through a sieve into a clean saucepan. Stir in cream and place over medium-low heat. Heat until hot, being careful not to bring to a boil or else the cream will curdle. Season with salt to taste; serve garnished with toasted slivered almonds.