In a heatproof bowl of a stand mixer, whisk the sugar, egg whites, and cream of tartar until combined.
Bring a pan of water to the boil. Place the mixer bowl over the simmering water, making sure it doesn’t touch the bottom.
Whisk over medium heat until a thermometer reads 160ºF / 70ºC, about 5 minutes.
Remove from the heat and add the vanilla extract.
Return the bowl to the stand mixer and whisk on high speed until stiff, glossy peaks form, about 8 minutes.
Preheat the broiler.
Using a cookie cutter, cut rounds of pound cake and place on a foil-lined baking sheet.
Top each cake round with a scoop of ice cream, then completely cover with the meringue mixture. Make sure both the cake and ice cream are fully sealed.
Place under the broiler until golden brown. Serve immediately.