Preheat oven to 350°
In a large batter bowl, combine flour, baking powder, salt and cardamom. Stir to mix. In another bowl combine very soft butter, the 1/2 cup of sugar, egg, lemon curd, lemon rind and milk. Stir to blend, then carefully add to the dry ingredients in the batter bowl. Stir to combine it all into a batter. Be careful to not overstir.
Spray a mini muffin pan with non-stick spray (I used coconut oil spray), then with a small cookie dough scoop, scoop and drop a ball into each cup of muffin pan. Cook for 10 - 12 min at 350°
While poppers are cooking in a small bowl, melt the cube of butter in microwave oven, then stir the lemon juice into butter. Place the 2/3 cup of sugar.
When poppers are done, remove from the oven and let cool for just a few minutes, then turn them out onto a sheet of waxed paper. One at a time, carefully dip the poppers in the butter, using a fork or slotted spoon to coat on all sides, then roll in the sugar. Let them cool on the waxed paper and serve. Or store in a plastic container for a little later.