Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, whisk together the flour, baking soda, baking powder, and salt. Set this mixture aside.
In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy. This will take about 3-4 minutes.
Beat in the egg and vanilla extract until fully combined.
Gradually mix the dry ingredients into the wet mixture until just combined. Be careful not to overmix!
Using a cookie scoop or a tablespoon, drop spoonfuls of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 12-15 minutes or until the edges are lightly golden. Remove from the oven and allow them to cool completely.
Once the cookies are cool, pipe or spoon a small amount of pastry cream onto the flat side of half the cookies, and then sandwich them with the other half.
In a microwave-safe bowl, combine the chocolate chips and vegetable oil. Microwave in 30-second intervals, stirring in between, until smooth.
Drizzle or spread the melted chocolate over the filled cookies. Allow the chocolate to set slightly before serving.