1. Preheat the oven to 375° F. Line a 24-cup mini muffin pan or 12-cup regular pan with paper liners.2. In a bowl, beat together the butter, 1/2 cup sugar, and lemon zest until combined. Add the yogurt and vanilla, beating until smooth. Beat in the eggs, one at a time, until combined. Add the flour, baking powder, and salt. Mix in the blueberries with 1 tablespoon flour. Swirl the jam into the batter; do not overmix.3. To make the cinnamon sugar (optional). Combine all ingredients in a bowl.4. Divide the batter evenly among the cups in the prepared pan, filling the cups most of the way full. Sprinkle the tops with cinnamon sugar (optional).5. Bake 18-22 minutes for mini muffins or 28-32 minutes for regular muffins, until just set.