Using a stand mixer with paddle attachment blend the flour, cocoa powder, brown sugar and salt on low speed until well combined.

Add the butter pieces and mix until mixture resembles course crumbs.

In a small bowl whisk together egg yolk, cream and vanilla, and add this to crumbly mixture, and blend until dough comes together fully.

Shape the dough into a flat disc, wrap well in plastic wrap and refrigerate for at least one hour.

Then, when sufficiently chilled remove from refrigerator and break off pieces of dough to roll a ball about 1 1/2 in diameter. Drop each ball into the mini tart pans. Using either a dough press or just your fingers, press dough into bottom and up sides of each tart pan.

Remove from oven and cool completely.

Combine sifting confectioners sugar, peanut butter and 4 tablespoons of cream. Beat with an electric mixer until smooth, adding additional cream as necessary to come to a creamy, yet thick texture.

Fill a piping bag fitted with a 1M tip with the peanut butter mixture and pipe into each cooled tart shell.

Drizzle caramel sauce over top of each tart if you wish.