Special equipment: 1-inch and 2-inch round cutters (for making Bobby Flay's Plain Doughnuts recipe)
For the topping: Preheat the oven to 325 degrees F.
Place the walnuts on a baking sheet in a single layer and toast until golden brown and fragrant, 5 to 7 minutes. Let cool slightly and chop. Put in a shallow dish with the bacon and mix together. Set aside.
For the apple cider glaze: In a small saucepot, add the apple cider, brown sugar, vanilla extract, cinnamon and a squeeze of lemon juice. Bring to a boil over high heat and then reduce to a simmer. Simmer until syrupy and reduced by half, about 10 minutes. Let cool.
Put the confectioners' sugar in a bowl and slowly pour in 1/4 cup of the glaze, a little at a time. Whisk together until smooth.
To top the doughnuts: Gently dip the top of each plain doughnut into the glaze and let any excess drip back into the bowl. Next, lightly dip the glazed tops into the chopped walnuts and bacon. Place on a wire rack to let set.
Bring the milk to a simmer in a 1-quart heavy saucepan, then remove from the heat and stir in the sugar and salt. Pour into a large bowl and let cool slightly.
While the milk is cooling, dissolve the yeast in 2 tablespoons warm water in a small bowl, stirring. Let stand for 5 minutes.
Stir the yeast mixture into the milk mixture along with the oil, lemon zest and eggs. Stir in 2 1/2 cups of the flour with a wooden spoon to make a very soft dough. Spread 1 cup of the flour on a work surface and put the dough on top, scraping it from the bowl with a rubber spatula. Knead the dough for about 5 minutes, incorporating all of the flour from the work surface and adding just enough additional flour (if necessary); the dough should be slightly sticky. Transfer the dough to an oiled large bowl and sprinkle lightly with additional flour. Cover the bowl with a clean kitchen towel and let the dough rise in a warm draft-free place until doubled in bulk, 1 to 1 1/2 hours.
Turn the dough out onto a floured surface and roll out with a floured rolling pin until 1 inch thick. Cut out rounds with a 2-inch cutter. To make ring shapes, cut out doughnut holes with a 1-inch cutter. Place on a baking sheet, cover the doughnuts with another kitchen towel and let rise in a warm place for 30 minutes.
While the doughnuts rise, heat about 10 cups vegetable oil in a deep 4-quart pot until it registers 365 degrees F on a deep-fry thermometer. Fry the doughnuts 2 at a time, turning once or twice, until puffed and golden brown, 2 to 3 minutes per batch. Transfer to paper towels to drain.