a deep-fry thermometer or deep-fryer; a large pastry bag
For the blueberry marmalade: In a medium saucepan, combine the blueberries, granulated sugar and 1/2 cup water and heat on high until boiling. Reduce to a simmer and cook until thick, approximately 30 minutes.
Preheat 3 inches oil in a deep-fryer or large Dutch oven to 350 degrees F. Line a sheet tray with a wire rack.
For the whipped yogurt: Combine the cream, yogurt and granulated sugar in a stand mixer and whip until firm peaks are reached.
For the funnel cake: In a large bowl, beat the eggs. Add the buttermilk, milk, scraped vanilla seeds and 1 cup water and beat until well blended. In another bowl, whisk together the flour, granulated sugar, baking powder and salt. Add the flour mixture to the egg mixture and stir until incorporated.
Ladle the batter into a large pastry bag and snip the tip with scissors when you are ready to fry. Squirt spirals of batter into the oil, layering the spirals until the desired size is reached, and fry until crispy on both sides, about 3 minutes per side. Remove and place on the wire rack. Repeat with the remaining batter.
Meanwhile, dust the funnel cake with powdered sugar and place on a plate. Cover each with marmalade and a spoonful of whipped yogurt. Serve immediately.