Preheat your oven to 350°F (175°C). Grease a round baking dish (usually about 9 inches or 23 cm in diameter) with butter.
In a large mixing bowl, combine the fresh cheese and sugar. Mix well until the sugar is fully incorporated into the cheese.
Add the eggs one at a time, mixing well after each addition. The mixture should become smoother and creamier as you add the eggs.
Stir in the lemon zest, ground cinnamon (if using), and vanilla extract (if using). These ingredients will add flavor to the quesada
Gradually add the all-purpose flour while continuously mixing. Make sure the flour is fully incorporated into the mixture, and you have a smooth batter.
Pour the batter into the greased baking dish, spreading it evenly
Bake in the preheated oven for about 40-50 minutes or until the top of the quesada is golden brown and the center is set. You can check for doneness by inserting a toothpick into the center; it should come out clean when the quesada is ready.
Once done, remove the quesada from the oven and let it cool in the baking dish for a while. Then, transfer it to a wire rack to cool completely.
Once the Quesada Pasiega has cooled, you can refrigerate it for a few hours or overnight before serving. This will help it set further and enhance the flavors.
Before serving, you can dust the top of the quesada with powdered sugar for a decorative touch.
Slice and serve chilled. Quesada Pasiega is often enjoyed as a dessert, snack, or even for breakfast with a cup of coffee.