Special equipment: a silicone baking mat; a candy thermometer; 8 to 10 parfait glasses
For the frozen yogurt: Strain the yogurt through a fine-meshed strainer for 2 hours. Put the strained yogurt, the sugar, cinnamon and vanilla extract in a blender and blend until the ingredients are incorporated, about 2 minutes.
Transfer the yogurt mixture to an 8-inch square baking dish and freeze until firm, about 1 hour.
Meanwhile, make the homemade walnut brittle: Line a baking sheet with a silicone baking mat and grease it liberally with 2 tablespoons of butter.
Bring the sugar and corn syrup to a boil in a large saucepan over medium heat, stirring constantly. Attach a candy thermometer to the side of the saucepan and cook until the mixture reaches 240 degrees F, about 6 minutes. Stir in the walnuts and cook until the mixture becomes golden-brown and reaches 300 degrees F, about 5 more minutes.
Remove the saucepan from heat, and stir in 1 stick butter, the vanilla extract, baking soda and salt¿the mixture will come to a vigorous bubble, then it will settle. Stir until the butter is fully melted and pour onto the silicone baking mat. Let the brittle cool completely, about 30 minutes. Break apart before serving.
To assemble the parfaits: Add a large spoonful of jam to each parfait glass, then a scoop of Frozen Yogurt, and top with a few pieces of Homemade Walnut Brittle.