Step 1

Heat oven to 350°F. Fold very long piece of aluminum foil in half lengthwise. Set in 13x9-inch baking pan, extending foil about 2 inches over edges. Line baking pan with additional foil.

Step 2

Combine 1 1/2 cups flour, 1/3 cup sugar and 1/4 teaspoon salt in bowl. Stir in melted butter until well combined. Press into prepared baking pan. Bake 20-22 minutes or until crust is light golden brown.

Step 3

Meanwhile, whisk 1 1/2 cups sugar, 3 tablespoons flour, 1 tablespoon cream of tartar and 1/4 teaspoon salt together in large saucepan. Whisk in 4 eggs and 6 egg yolks until well combined but not airy. Whisk in lemon zest and juice.

Step 4

Cook over medium-low heat, stirring constantly, 8-12 minutes or until mixture thickens and reaches 160°F. Remove from heat; stir in butter, 2 pieces at a time, allowing butter to melt before adding more. Strain filling through fine-mesh strainer set over bowl. Set bowl aside.

Step 5

Beat 6 egg whites and 1 teaspoon cream of tartar in bowl at low speed until foamy. Beat at high speed, gradually adding 3/4 cup sugar, 3-4 minutes or until stiff peaks form and mixture is glossy.

Step 6

Pour hot lemon filling into baked crust. Spread meringue over hot filling, completely sealing to edge of pan.

Step 7

Bake 18-22 minutes or until meringue reaches 160°F and is lightly browned.

Step 8

Cool 3-4 hours at room temperature. Remove from pan using foil ends for easier cutting and serving.