In the bowl of a stand mixer fitted with the paddle attachment, beat butter, confectioners’ sugar, and ¼ teaspoon salt at medium speed until creamy, 1 to 2 minutes, stopping to scrape sides of bowl. Add 1 egg yolk; beat until well combined. Beat in ¼ teaspoon vanilla.

In a medium bowl, whisk together flours. With mixer on low speed, gradually add flour mixture to butter mixture, beating just until a dough forms.

Spray 8 (2½x-9/10 inch) fluted round tart pans with baking spray with flour; place on a rimmed baking sheet.

Divide dough into 8 portions, and shape into balls. Press 1 dough ball into bottom and up sides of 1 prepared tart pan; trim any excess dough. Repeat with remaining dough and remaining tart pans.

In another medium bowl, whisk together remaining 3 egg yolks.

In a small saucepan, combine ¼ cup water, granulated sugar, evaporated milk, remaining ½ teaspoon vanilla, and remaining ¼ teaspoon salt. Cook over medium heat until steaming and sugar dissolves. Gradually whisk sugar mixture into egg yolks until well combined.

Position oven rack in bottom third of oven. Preheat oven to 400°F.

Place a fine-mesh sieve over a large liquid-measuring cup or wide-mouthed pitcher. Strain egg yolk mixture through prepared sieve; discard any solids. Divide strained mixture among prepared crusts.

Bake until crust is lightly browned, 10 to 12 minutes, rotating pan halfway through baking. Reduce oven temperature to 350°F, and bake just until edges of filling start to puff, about 5 minutes more. With oven still on, open oven door about 2 inches; bake until filling is set, a wooden pick inserted in center stands up straight, and an instant-read thermometer inserted in center registers at least 175°F, 5 to 7 minutes more. Let cool in pans for 15 minutes. Remove from pans, and serve warm or at room temperature.