Preheat the oven to 400 degrees F (200 degrees C). Grease a 12-cup muffin tin or line with paper liners.
Beat 3/4 cup sugar and butter together in a mixing bowl using an electric mixer until creamy. Add egg and mix well.
Sift flour, baking powder, and salt together in a small bowl. Add flour mixture and milk alternately to butter mixture until combined. Stir in vanilla extract. Gently stir in strawberries.
Spoon batter into the prepared muffin cups. Combine 3 teaspoons sugar and cinnamon in a small bowl and sprinkle over tops of muffins.
Bake in the preheated oven until a toothpick inserted into the center of a muffin comes out clean, 20 to 25 minutes.