Preheat an oven to 200ºC Butter standard muffin tins. In a large bowl stir and toss together the flour, baking powder, baking soda and salt. Set aside. In a medium bowl whisk together the sugar, milk, sour cream, oil, egg and orange zest until mixed; stir in the strawberries. Add to the combined dry ingredients and stir just until blended. Place a spoonful of batter in each prepared muffin cup. Top each with a scant teaspoon of strawberry jam. Spoon the remaining batter over the jam, filling each cup about two-thirds full. Bake until a toothpick inserted in the center of the muffin comes out clean, 15-18 minutes. Cool in the tins for 5 minutes, then remove. Makes about 16 standard muffins.