Heat apple cider in a small saucepan over high heat. Bring to a boil; reduce heat and simmer, stirring occasionally, until reduced to 1 cup, about 15-20 minutes. Let cool completely.
In a large bowl, combine flour, brown sugar, baking powder, salt, baking soda, nutmeg and remaining 1 1/2 teaspoons cinnamon.
In a large bowl, whisk together butter, eggs and apple cider.
Pour mixture over dry ingredients and stir using a rubber spatula just until moist. DO NOT OVERMIX. Cover and place into the refrigerator until chilled, about 1 hour. Divide dough in half.
Working on a lightly floured surface, roll dough into 1/2-inch thick rounds; cut out rounds with a 2 1/2-inch cutter.
Heat vegetable oil in an electric fryer. Alternatively, use a large stock pot or Dutch oven and heat to 325°F by using an instant read candy thermometer to gauge.
Working in batches, add donuts to the electric frying pan and cook until evenly until golden and crispy, about 1 to 2 minutes per side. Transfer to a paper towel for 30 seconds to blot, then roll in cinnamon sugar mixture to coat.
Serve warm with piping hot coffee and plenty of napkins.