Step 1 Place one-half cup sugar with the corn syrup in a pot with just enough water, about 2 tablespoons, to wet the sugar to a wet sand consistency. With a pastry brush dipped in water, clear off the edges and sides of the pot to be sure there are no loose sugar crystals. Cook the mixture over medium-low heat until it turns a dark amber color. Pour it into the bottoms of the four ramekins and allow to cool.
Step 2 Heat the oven to 500 degrees. Toast the hazelnuts until golden brown. Remove and allow to cool. When cooled, put the nuts into a food processor with one-quarter cup sugar and process until finely ground.
Step 3In a medium pot, bring the milk and cream to a boil. Add the hazelnut mixture, cover and steep for one hour off the heat.
Step 4In a large bowl, whisk the yolks, egg and remaining one-quarter cup sugar. Reheat the milk mixture to boiling. Pour the milk mixture into the egg mixture in a steady stream, whisking constantly. Strain through a chinois or cheesecloth-lined strainer.
Step 5Heat the oven to 300 degrees. Pour the mixture into the ramekins, then place the filled ramekins into a baking pan. Fill the pan with a one-inch water bath of boiling water.
Step 6Cover the pan with foil and bake for 25 minutes, or until the edges are set but the centers still jiggle. Let cool and refrigerate for at least 3 hours or overnight.