Preheat oven to 300°F (149°C). Line the bottom and sides of an 8-inch square baking pan with parchment paper, leaving an overhang on 2 sides to easily lift the bars out of the pan before cutting. Set aside.

In a medium bowl, whisk the graham cracker crumbs and sugar together. Add the melted butter and stir until combined. Press evenly into the prepared baking pan. Bake for 8 minutes. Remove from the oven and set aside to cool slightly.

In a large bowl using a handheld or stand mixer fitted with a whisk attachment, beat the cream cheese on high speed until completely smooth, about 1 minute. Add yogurt and beat on medium-high speed until completely combined. Scrape down the sides and up the bottom of the bowl with a silicone spatula and beat again as needed to combine. Beat in the eggs and egg yolk. Once combined, add the sugar, lemon juice, lemon zest, and vanilla extract and beat until everything is combined and no lumps remain. Filling is thin. Pour filling into the crust—it’s ok if the crust is still slightly warm.

Bake for 34–38 minutes or until the middle is no longer wobbly. A little jiggle is ok—the bars will continue to set up as they chill in the refrigerator, so you don’t need to bake them until the center is perfectly solidified. Don’t over-bake these bars, or the surface may crack.

Set the pan on a cooling rack and cool for 1 hour, then transfer to the refrigerator to chill for 3–4 hours or even overnight.

Once chilled, lift the bars out of the pan using the parchment overhang on the sides and cut into bars. For neat bars, I use a very sharp knife and wipe it clean with a paper towel after each cut.

Cover and store leftover bars in the refrigerator for up to 5 days.