PREPARE THE CRUST

1. Position a rack in the center of the oven and preheat to 325°F.
2. Grease an 8×8-inch baking pan and line with parchment paper, leaving an overhang on all sides for easy removal. Set aside.
3. In a medium bowl, whisk together the gluten-free 1:1 flour, almond flour, granulated sugar, cornstarch, and salt.
4. Add the melted butter, vanilla extract, and almond extract, and stir until a cohesive dough forms.
5. Press the dough firmly into the bottom of the prepared pan, creating an even layer. Use an offset spatula to smooth the surface and create clean edges.
6. Bake for 22–25 minutes, or until the crust is set with a matte finish and lightly golden edges.

MAKE THE LEMON FILLING

1. Place the cubed butter in a heat-safe bowl and set a fine mesh strainer over the top. Set aside.
2. In a large bowl, combine the sugar and lemon zest. Rub the zest into the sugar with your fingers until fragrant.
3. Add the cornstarch, gluten-free 1:1 flour, and salt, and whisk to combine.
4. Add the eggs and egg yolks, and whisk until fully incorporated.
5. Slowly pour in the Meyer lemon juice and regular lemon juice, whisking until smooth.
6. Transfer the mixture to a heavy-bottomed saucepan and cook over medium-low heat, whisking constantly, until thickened and the mixture reaches 170°F on an instant-read thermometer, about 8–12 minutes. The mixture should not come to a full boil, though light bubbling around the edges is normal.
7. Remove from the heat and immediately pour through the prepared strainer into the bowl of butter. Use a rubber spatula to press the mixture through the strainer if needed.
8. Stir until the butter is fully melted and the mixture is smooth.

BAKE THE BARS

1. Pour the warm lemon filling over the warm crust, spreading gently if needed to create an even layer.
2. Tap the pan lightly on the counter to release any air bubbles.
3. Bake for 15–18 minutes, checking around 12 minutes. The edges should be set, and the center should have a slight jiggle when gently shaken.
4. Remove from the oven and cool at room temperature for 1 hour.
5. Transfer to the refrigerator and chill uncovered for at least 4 hours, or until fully set.

FOR SERVING

1. When ready to serve, lift the bars out of the pan using the parchment overhang. Slice into squares with a sharp knife, wiping the blade clean between cuts.
2. Dust with powdered sugar just before serving.

Store the bars in an airtight container in the refrigerator for 4–5 days.