Heat oven to 350°F; line sheets with parchment.
Cream butter and sugar in a large bowl until fluffy, about 3 minutes.
Beat in egg and vanilla.
Whisk flour, baking powder, and salt separately; gradually mix into wet ingredients until just combined.
Put sparkling sugar in a shallow bowl. Roll dough into 1-inch balls; coat completely in sugar.
Place 2 inches apart on sheets; leave round or gently flatten with a glass.
Bake 10-12 minutes until edges just set and centers remain slightly soft.
Cool on sheets 5 minutes, then completely on a rack.