Combine cake flour and bread flour in equal parts to achieve the ideal balance of tenderness and structure; cake flour alone produces too-delicate dough while bread flour alone creates density.

Heat caramel to 160-165°F before filling to ensure it sets slightly but remains gooey inside; hotter caramel will be too firm, cooler will leak during frying.

Allow eggs and butter to come to room temperature before mixing to ensure proper emulsification and a smoother, more uniform dough that rises evenly.

Pinch and seal the dough opening tightly with damp fingers after filling to prevent caramel from leaking during frying; a weak seal is the leading cause of filling loss.

Maintain oil at precisely 350°F using a thermometer; temperatures below 340°F produce greasy bomboloni, while above 360°F will burn the exterior before the interior cooks through.