To make blueberry filling, place blueberries in a small saucepan and heat over medium heat. Let heat until juice begin to extract from blueberries and fill the bottom of the pan. Stir frequently, add in sugar and cornstarch. The sauce will begin to thicken and if should be consistency of pudding (the sauce will thicken as it cools.) If the sauce is too thick before cooling, add a spoonful of sugar. Scrap into a separate bowl and set aside to cool.
Preheat oven to 350˚
In a small bowl, sift dry ingredients and set aside.
In a medium bowl (or a bowl of a stand mixer) combine butter and sugar, beat until light and fluffy- about 3 minutes. Add in egg and vanilla, continue to beat until incorporated. Add 1/3 of the dry ingredients followed by half of the milk. Beat until just combined. Scrap down sides and repeat. Add remaining flour and mix until batter is combined- don\’t over mix.
Divide batter into 12 cupcakes and bake for 18-20 minutes or until cupcake springs back when pressed. Remove from pan and let cool.
Once cupcakes are cool, combine butter, powdered sugar, lemon zest, and lemon juice in a bowl. Using a paddle attachment, beat frosting, adding enough of the whipping cream to achieve a spreadable consistency (you don\’t want the butter cream too soft or too firm.)
To fill the cupcakes, scoop filling into large piping bag with a coupler on the end. Cut an X into the cupcake and place the end of the coupler- squeeze until blueberry filling comes out of the top of the cupcake (cupcake will hold together as long as you don\’t over fill it!)