Set your oven to 375ºF and line a muffin tin with paper liners or grease well.
In a medium bowl, whisk together flour, sugar, baking powder, cinnamon, and salt until combines.
In another bowl, whisk together the melted butter, milk, strawberry yogurt, and egg until smooth.
Add the wet ingredients to the dry ingredients, stirring gently until just combined. Be careful not to overmix.
Fold in the chopped fresh strawberries, ensuring even distribution throughout the batter.
Drop a tablespoon of batter into prepared muffin cups. Spoon a small dollop of strawberry jam and top evenly with another tablespoon of batter.
Sprinkle each muffin with a mix of sanding sugar and cinnamon for a sparkly, crunchy finish.
Bake for 15-18 minutes, or until a toothpick inserted in the center comes out clean. Let muffins cool slightly in the tin before transferring to a wire rack. Serve warm or at room temperature.