Preheat your oven to 375°F (190°C). This takes about 10 minutes. Spray a standard 12-cup muffin tin with nonstick cooking spray, making sure to coat the bottom and sides of each cup evenly. The spray prevents sticking and makes cleanup easier.

In a large mixing bowl, combine 2 cups flour, 3/4 cup sugar, 2 teaspoons baking powder, 1 teaspoon cinnamon, and 1/4 teaspoon salt. Whisk these dry ingredients together for about 1 minute until evenly blended. Checkpoint: You should see no lumps of baking powder and the cinnamon should be distributed throughout the dry mixture.

In a separate small bowl, beat 1 large egg until it's broken up and well mixed, about 30 seconds. Add the beaten egg, 1 cup unsweetened applesauce, and 1/2 cup melted butter to the dry ingredients. Stir by hand with a wooden spoon or spatula until just combined, about 1–2 minutes. Do not overmix. Checkpoint: The batter should look lumpy and shaggy; some streaks of flour are fine. Overmixing makes tough, dense muffins.

Using a standard ice cream scoop or spoon, divide the batter evenly among the 12 muffin cups, filling each cup about three-quarters full (roughly 1/4 cup batter per muffin). This takes about 2 minutes and ensures even-sized muffins that bake consistently.

Sprinkle 1/4 to 1/2 teaspoon of crystal sugar over the top of each muffin. The sugar adds a subtle crunch and sweet sparkle to the finished muffin. This step takes about 1 minute.

Place the muffin tin in the preheated 375°F oven on the middle rack. Bake for 18 to 20 minutes. The muffins are done when the tops are golden brown and a toothpick inserted into the center of one muffin comes out clean (with no wet batter clinging to it). Checkpoint: The muffin tops should have a light golden-brown color and spring back when lightly touched.

Remove the muffin tin from the oven carefully using oven mitts. Let the muffins cool in the pan for 3–5 minutes. This allows them to set slightly and become easier to remove without breaking. After 5 minutes, run a thin knife around the edge of each muffin and gently turn the tin upside down or lift each muffin out with a fork.

Transfer the warm muffins to a wire cooling rack and let them cool for at least 10–15 minutes before serving. This stops the cooking process and allows the crumb to set properly.