In a separate bowl, whisk together eggs, milk, sugar, butter and vanilla.
Add egg mixture to dry ingredients using light strokes. Do Not Over Mix: batter will be lumpy. Fold in blueberries and nutmeg.
Divide the batter among muffin cups and fill to the top. Divide the Hazelnut Streusel (see recipe) among the muffin tops. Bake at 400 degrees for 15 to 20 minutes. Let cool for 5 minutes before removing from pan.