The Dutch doughnut traditionally eaten on New Year's Eve is the oliebol, plural oliebollen.
An oliebol is a ball of yeast-raised dough dropped into hot oil and deep-fried. The batter commonly contains flour, eggs, milk, yeast, and salt, with raisins, currants, or sultanas often mixed in. Finished oliebollen are usually dusted with powdered sugar and served warm or at room temperature.
The name literally means “oil ball,” describing both its round shape and cooking method. Oliebollen are sold widely from seasonal street stalls and temporary food stands in the Netherlands during the winter holiday period. An apple-filled variation, the appelbeignet, is related but is not the standard answer to this question.
The treat belongs to a broader family of fried dough foods found across Europe and elsewhere. Poffertjes are small, fluffy Dutch pancakes, while stroopwafels are thin waffle cookies joined with syrup; neither is the traditional New Year's Eve doughnut. Oliebollen are especially associated with celebrating the transition into the new year.