Place a large sauté pan over medium-high heat. Add the oil or butter, onion, pepper, and the white part of the scallions. Season with salt, reduce the heat to medium-low and sauté until the onions turn translucent and lightly golden, about 10–12 minutes.

Meanwhile, using a sharp knife, cut the kernels off of 4 ears of corn. To do this, hold the corn cob upright on a cutting board and using a sharp knife, slice downward between the kernels and the cob, keeping the blade as close to the cob as possible. Rotate the cob and repeat until all the kernels have been removed. 

On a box grater, grate the remaining 4 ears of corn. Keep the corn kernels and grated corn in separate bowls.

Stir in the cinnamon (if using), cumin, and corn kernels into the onion mixture and sauté over medium heat, stirring occasionally, for 10 more minutes.

Stir in the grated corn and ½ cup water, cover and let simmer for 20 minutes, stirring periodically. Remove the lid and keep cooking until the mixture has reduced and the vegetables are cooked through. Transfer to a bowl and refrigerate until completely cool.

While the filling is cooling down, prepare the dough: In a small bowl, stir together the warm water and salt until the salt is dissolved.

Place the flour in a medium bowl, make a well in the center, and pour in the melted butter. Gradually add the salt water while mixing with a wooden spoon. When a shaggy dough forms, transfer to a work surface and knead until a smooth, soft dough is reached, about 3–4 minutes. Be careful not to overwork it. Wrap the dough tightly with plastic wrap and let rest for 1 hour at room temperature.

Preheat the oven to 375°F.

Divide the dough into 20 ping-pong sized balls, 40 grams each. Cover the balls with plastic and work with one at a time. Using a rolling pin, roll each ball into a circle about 5-6 inches wide and ⅛ inch thick. Add a little flour to the work surface only if the dough sticks. Place the rolled-out empanada discs flat on a surface. They can slightly overlap, but do not stack them. Keep covered with plastic wrap. 

Remove the corn filling from the refrigerator and mix in the green parts of the scallions. Taste and adjust salt if needed.

Place 1½–2 tablespoons of filling in the center of each circle. Fold into a half-moon shape, leaving a ½-inch border. If the dough doesn’t stick, using your finger, brush a little water on the inner border of the dough. Press the edges and crimp to seal, either by pinching and folding the edge or by pressing a fork along the rim. Arrange the empanadas on a parchment-lined baking sheet, leaving a small space between them. Cover with plastic wrap until you finish folding the rest.

Whisk the egg with 1 tablespoon of water and brush over the empanadas. Bake until golden, 30–35 minutes. Let the empanadas cool for a few minutes, then serve.