1.

Make the filling: Lightly grease a sheet pan with butter and set aside. Combine water, sugar, corn syrup or honey, and butter (if using) in a medium pot. Turn the heat to medium and use a heat resistant spatula to stir gently until the sugar has dissolved. Once mixture starts to bubble, stop stirring and let simmer undisturbed.

Cook until mixture has a pale golden color, about 300°F on a candy thermometer (a thermometer useful but not necessary, you can judge the mixture purely by color).

Shut off heat and stir in peanuts with a spatula. Pour mixture onto sheet pan and use spatula to spread it as thin as you can manage.

When the brittle has cooled completely, transfer it to a cutting board and chop roughly with a knife.

Put chopped brittle into a food processor and pulse until brittle has been ground into small chunky pieces. Then let the food processor run continuously until the mixture begins to turn into a paste.

Shut off processor, add peanut butter, then replace the lid; process until the mixture is homogeneous. Then, with mixer still running, slowly drizzle in vanilla and oil.

The mixture should be a thick paste, but fluid enough to squeeze through a piping bag. If the mixture seems too thick, drizzle in more oil, a tablespoon at a time, until it has thinned sufficiently.

Transfer mixture to a pastry bag fitted with a large, plain tip. Set aside until needed.