In a mixing bowl, whisk together the eggs, sugar, melted butter, rum (if using), lemon zest, and a pinch of salt until well combined.

Gradually add the flour to the mixture and knead the dough until smooth and elastic. If the dough is too sticky, add a little more flour.

Roll out the dough on a floured surface until it's about 1/4 inch thick. Cut the dough into strips about 1 inch wide and 4-5 inches long.

Make a small cut in the center of each strip and pull one end of the strip through the cut to create a twisted shape.

Heat the vegetable oil in a deep frying pan or pot to 350°F (180°C).

Fry the twisted dough strips in batches until they are golden brown and crispy, about 2-3 minutes per side. Drain them on a paper towel-lined plate.

Dust the kroštule with powdered sugar while they're still warm.