Pour enough oil into a large Dutch oven or pot to cover the bottom by 2 inches. Heat over medium heat until the oil reaches 365F to 375F. Line a rimmed baking sheet or serving plates with paper towels.
Meanwhile, in a large bowl, whisk together the milk, eggs, sugar, and vanilla until well combined. In another bowl, whisk together flour, baking powder, and salt. Stir the flour mixture into the milk mixture until combined.
Using your finger to cover the spout hole, ladle about 1/3 cup of batter into a funnel. Starting in the center with the funnel a few inches from the surface of the oil, remove your finger and move the funnel in a circular or swirling motion around the oil, drizzling the batter to create about a 6-inch round.
Fry until deep golden brown, flipping over when needed, about 1 to 2 minutes per side. Remove with a slotted spoon or spider and let drain on paper towels.
Dust well with powdered sugar and serve hot.
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Notes
A candy thermometer is a great tool to help get the temperature of the oil right. If the oil is too hot, the exterior will burn before the interior cooks, and if the oil is not hot enough, the funnel cake will absorb too much oil as it cooks, making it greasy.
If you are not using a scale to measure the flour, be sure to fluff the flour with a spoon and then sprinkle it into the measuring cups before leveling it off with a knife. This method is the best way to measure flour without overpacking the cup. If you add too much flour, it will cause the batter to be too thick to pour through a funnel.
If you don’t have a funnel, you can use a measuring cup or a squeeze bottle to pour your batter into the oil.
Placing the freshly fried cakes on a paper towel before serving can help absorb extra oil.
A Dutch oven is ideal for frying. The cast iron will help the temperature of the oil from fluctuating too much and help keep the cooking even. If you do not have one, use a large heavy-bottomed pot with high sides to avoid splatter.