To substitute almond milk for regular milk, use the same amount called for in the recipe and use unsweetened almond milk. (Some brands of almond milk have added sugar or other sweeteners which can affect the flavor of your recipe.) For buttermilk, which is tangier than milk, add a little squeeze of lemon or a splash of vinegar. The almond milk won't be as thick, but the acid helps replicate the flavor of buttermilk.
For more information on ingredient substitutions, see our Ingredient Substitution Guide.
Recipe: Chocolate Layer Cake