Preheat oven to 350°F (180°C). Spray an 8-inch square baking pan with cooking spray. Line pan with parchment paper, letting excess extend over sides of pan.

In the bowl of a stand mixer fitted with the paddle attachment, beat cream cheese at medium speed until smooth and creamy, about 2 minutes, stopping to scrape sides of bowl. Add condensed milk, ¼ cup (31 grams) flour, lemon juice, 1 teaspoon (3 grams) salt, and 1 teaspoon (4 grams) vanilla; beat at medium speed just until combined, about 1 minute, stopping to scrape sides of bowl. Beat in egg yolks just until combined. Refrigerate until ready to use.

In a large bowl, whisk together granulated sugar, melted butter, and remaining 1 teaspoon (4 grams) vanilla.

In a medium bowl, whisk together oats, baking powder, pie spice, remaining 1⅔ cups (208 grams) flour, and remaining 1 teaspoon (3 grams) salt. Gradually stir oat mixture into sugar mixture until combined. Press 1¼ cups (344 grams) sugar mixture evenly into bottom of prepared pan.

Bake until edges are golden brown and center is dry, lightly golden, and just set, 18 to 24 minutes. Let cool in pan on a wire rack for at least 30 minutes. Leave oven on.

Spread cream cheese mixture onto prepared crust; spoon Spiced Apple Filling on top. Crumble remaining sugar mixture in large clumps over filling, leaving a bit of filling exposed.

Bake until topping is light golden brown and set, 30 to 38 minutes, loosely covering with foil during last 4 minutes of baking to prevent excess browning. Let cool in pan for 30 minutes. Refrigerate in pan, uncovered, for at least 4 hours or up to overnight.

Using excess parchment, remove from pan, and cut into bars; let stand at room temperature for 30 minutes before serving. Garnish with confectioners’ sugar, if desired.