We use stainless steel tumblers just like the classic soda shops and it always turns out perfect. To combine properly with the sugar, butter should be somewhere between 65°F and 70°F. Drop three or four butter slices into the blender. Word to the wise: Never use an immersion blender in a shallow pan. It’s important to use softened butter, which sometimes people are too impatient to do. You could possibly mix batter in the blender.
Instead of creaming the butter and sugar, I've whizzed the eggs and sugar, then added soft butter, then the dry ingredients.
of the sugar.