01 - Preheat oven to 350°F. Line a 9x5-inch loaf pan with parchment paper, leaving overhang for easy removal.
02 - Cream butter and sugar until fluffy. Add eggs one at a time, then vanilla. In a separate bowl, whisk flour, baking powder, and salt. Alternate adding dry ingredients and milk to the butter mixture, mixing until just combined.
03 - Pour batter into prepared pan, spread evenly, and bake for 20-22 minutes until a toothpick comes out clean. Cool completely in the pan.
04 - Remove cooled cake from pan. Clean and re-line the loaf pan with parchment. Place cake back in pan and spread softened ice cream evenly over it. Smooth surface, cover with plastic wrap, and freeze at least 4 hours until firm.
05 - Beat egg whites and cream of tartar until soft peaks form. Gradually add sugar, beating until stiff, glossy peaks develop. Fold in vanilla extract.
06 - Remove ice cream cake from freezer using parchment. Invert onto baking sheet and spread meringue evenly over top and sides, sealing edges. Increase oven to 500°F or use broiler. Bake 2-3 minutes or torch until golden. Serve immediately or freeze.