Remove 8 whole outer cabbage leaves.
Bring a saucepan filled with 2 inches of water to a simmer. Remove from heat. Melt half the chocolate in a heatproof bowl set over saucepan, stirring gently with a rubber spatula, until chocolate reaches 118 degrees on a candy thermometer. (Watch the chocolate carefully, since the time it takes for different chocolates to heat and cool can vary.) Remove from heat.
Add remaining unmelted chocolate to bowl, and stir until chocolate cools to 84 degrees. (Remove any unmelted pieces with spatula.) Return bowl to saucepan, and let stand, stirring, until chocolate registers 88 degrees to 90 degrees.
Immediately coat outside of 1 cabbage leaf with a thick layer of chocolate using a pastry brush. Drape leaf, chocolate side up, over a small inverted bowl to keep the rounded shape of the leaf. Repeat with remaining leaves and chocolate. Refrigerate leaves on bowls until set, about 30 minutes.
Gently grasp outer edge of each chocolate leaf with your fingers, and carefully tear off pieces of cabbage. Use kitchen scissors to cut away any tough, thick pieces of cabbage. Arrange chocolate bowls on plates, and fill with scoops of ice cream.
Chocolate bowls can be refrigerated for up to 2 days.