Preheat your oven to 350°F (175°C) and prepare a baking pan by greasing it well to prevent the cake from sticking.

Soak eggs in warm water for about 10 minutes to bring to room temperature.

Cream together the unsalted butter and sugar with an electric mixer on medium speed for 4-5 minutes until light and fluffy.

Add in the room temperature eggs and vanilla extract, mixing until fully combined and smooth.

Sift together the flour, baking powder, instant pudding mix, and salt in a separate bowl.

Gradually add the dry mixture to the wet ingredients, alternating with cream soda, mixing until just combined.

Pour the batter into the prepared pan and bake for 40-45 minutes or until a toothpick comes out clean.

Let the cake cool in the pan for 30 minutes, then transfer to a wire rack to cool completely.

For the mousse, whisk together the instant pudding mix and heavy cream until thick and fluffy, about 5 minutes.

To make the frosting, beat cream cheese and butter until smooth, gradually mix in powdered sugar and cream soda until fluffy.

Cut circles from the cooled cake using a cookie cutter for the base of the jars.

Layer the cake circles, butterbeer mousse, and frosting into jars, finishing with frosting on top and optional sprinkles.