To bake these poppy seed muffins, preheat oven to 400° F. Line one 12-cup and one 6-cup muffin pan with cakeliners or spray pans with non-stick cooking spray. Set aside.
Stir baking mix, sugar(s), (nuts, lemon peel or spices, if applicable) until blended. Beat eggs, oil, and buttermilk with electric mixer until blended. Add to dry ingredients and stir just until moistened. (Batter will be lumpy) Stir in filling. Spoon batter into prepared muffin cups, filling cups until approximately two-thirds full.
Bake 15 to 18 minutes or unitl toothpick inserted in center of muffin comes out clean. Cool in pans on wire racks. 1 minute. Remove poppy seed muffins from pans and serve warm or cool completely on racks.