Here's a whimsical weekend project for dessert lovers. It doesn't require much in the way of special equipment — just an electric mixer and a candy thermometer. If you have a Silpat, that's helpful, too, but not absolutely necessary.
Place the yolks in the bowl of an electric stand mixer and beat on medium speed until they are thick and form a ribbon when dropped from the whisk. Leave the mixer running. Place the sugar and corn syrup in a pot and cook to 255 degrees as measured by a candy thermometer.
Pour the hot sugar slowly into the mixing egg yolks. Add the gelatin and mix to combine. Add the warm peanut butter. When the mixture cools to room temperature, fold in the whipped cream. Pour into small 3- to 4-ounce rectangular molds and freeze. Alternatively, the mixture can be poured into a muffin tin lined with plastic wrap.
Combine the sugar, butter, corn syrup, and water in a medium-sized pot and bring to 300 degrees as measured by a candy thermometer. Stir in the baking soda and salt, then fold in the nuts. Spread thinly on a Silpat or parchment paper. Let cool and place in an airtight container.
Place the sugar in a clean pot and cook to a dark caramel. In another pot, bring the cream to a boil. Deglaze the sugar with the hot cream. Return to a boil and then strain. Stir in the salt and let cool to room temperature.
Preheat the oven to 350 degrees.
In a large pot, melt together the butter, chocolate, and brown sugar. Stir in the remaining ingredients. Pour into a lined baking sheet and bake until the center starts to crack and feels somewhat dry, about 30-35 minutes. Do not overbake. Let cool and cut into oblong rectangles.
In a medium-sized pot, bring the cream and corn syrup to a boil. Place the chocolate and peanut butter in a bowl and pour the cream mixture over the top; let sit for a few seconds. Mix well.
Glaze the peanut butter parfait with the slightly warm peanut butter chocolate glaze. Grind up some of the peanut brittle and sprinkle around the edges. Grind up some of the brownie into a crumble. Serve with the salted caramel sauce, extra honey-roasted peanuts, and some of the brownie bits.