Step 1

Whisk brown sugar and 1 1/2 teaspoons cinnamon together in a shallow bowl. Dip each piece of butter into cinnamon-sugar mixture to coat completely. Place butter pieces in a single layer on a parchment paper-lined baking sheet. Freeze until hard, 8 hours to overnight.

Step 2

Stir 1 cup flour, 2 teaspoons cinnamon, baking powder, and salt together in a bowl. Beat buttermilk, eggs, and white sugar together in another bowl; add flour mixture to buttermilk mixture and beat until smooth. Gradually stir remaining flour into buttermilk mixture until desired batter consistency is reached.

Step 3

Heat oil in a deep-fryer or large saucepan to 375 degrees F (190 degrees C).

Step 4

Poke a toothpick into the center of each frozen piece of butter. Dip butter into batter to coat completely.

Step 5

Working in batches, carefully drop coated butter pieces into hot oil and cook, turning occasionally, until golden brown and puffed, about 2 minutes. Transfer fried butter to a paper-towel lined plate and dust with confectioners' sugar.