• Pre-heat oven to 350 degrees.
• In the bowl of a stand mixer (or in a large bowl with a hand mixer), cream together butter, brown sugar, and granulated sugar until light and fluffy, about 2-3 minutes.
• Mix in egg and vanilla extract until combined.
• In a separate medium-sized bowl, whisk together cake flour, baking powder, and salt.
• Add half of flour mixture into mixing bowl and blend until just combined.
• Mix in coffee creamer and milk.
• Add the remainder of the flour mixture to the mixing bowl and blend until just combined.
• Lightly spray whoopie pie pan with oil or cooking spray.
• Spoon batter into whoopie pie pan cavities, using about 1 ½ T to fill cavities ⅔ of the way full. Make sure batter is spread to edges of pan.
• Bake for 7-9 minutes, until cakes are just starting to turn golden around edges and a toothpick comes out clean.
• Let cakes cool in pan for at least 5 minutes. Remove cakes from pan and cool completely on baking rack.
• Once cakes are cooled, fit pastry bag with a standard round pastry tip and spoon custard filling into bag. Pipe generous amount of custard filling onto one whoopie pie cake round and sandwich with another.
• Spoon chocolate ganache over the top of each whoopie pie and allow to drip down the edges.

Custard Filling:

• In a medium-sized saucepan, bring coffee creamer and milk to the simmer.
• In a separate medium-sized bowl, whisk together egg yolks, granulated sugar, and cornstarch.
• Pour half of the creamer/milk mixture into the egg yolks, continuously whisking.
• Then pour back into creamer/milk saucepan and continue to whisk for about 5 minutes while mixture thickens.
• Remove from heat and stir in butter.
• Pour pastry cream into a bowl, cover with plastic wrap (so plastic wrap is touching top of pastry cream) and let cool completely.
• Mix green food coloring into pastry cream if desired.

Chocolate Ganache:

• Place dark chocolate in a medium-sized bowl.
• Heat coffee creamer in a small saucepan over medium-low heat.
• When creamer is very hot (but not boiling), pour over chocolate. Stir gently until smooth.
• Allow to cool slightly before using.