HEAT oven to 225°F. BEAT egg whites and cream of tartar in mixer bowl with whisk attachment on high speed until foamy. BEATING constantly, ADD sugar, 2 Tbsp. at a time, until whites are glossy and stand in stiff peaks.

FOLD IN ground almonds. SPOON into pastry bag fitted with large fluted or plain tip. PIPE meringue onto baking sheets lined with parchment paper or aluminum foil. Sprinkle with sliced almonds.

BAKE in 225°F oven until firm, about 1 hour. TURN OFF oven. LET DRY in oven, with door closed, until cool and crisp, at least 1 hour.