Heat olive oil in a large skillet over medium heat.

Add chopped peppers, pul biber, and onions to the skillet.

Season with salt and pepper.

Cook, stirring occasionally, until vegetables are softened, about 10 minutes.

Add ground beef and cook until the liquid has evaporated, about 10 minutes.

Season with salt and pepper.

Continue cooking, stirring occasionally, until vegetables are fully softened, about 15 minutes.

Transfer the beef and vegetable mixture to a bowl and let cool slightly.

Preheat oven to 400 degrees F (200 degrees C).

Lightly oil a 9x13 inch glass baking dish.

In a medium bowl, whisk eggs with milk and 1/2 cup canola oil.

Lay a sheet of yufka on a work surface and brush with egg mixture.

Repeat with another sheet of yufka, creating a stack of two sheets.

Transfer the yufka stack to the prepared baking dish.

Spread one-third of the beef mixture evenly over the yufka.

Repeat the layering process twice more with the brushed yufka sheets and beef filling.

End with a stack of brushed yufka sheets on top.

Trim any overhanging yufka and tuck it under itself to create a neat edge.

Brush the remaining egg mixture evenly over the top of the borek.

Sprinkle nigella sativa seeds over the top.

Bake until deeply golden and sizzling, about 45 minutes.

Let the borek rest for 20 minutes before cutting into squares and serving.