Blueberry Lemon Bars with Meringue Topping

Stages of cooking

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1. Combine flour, almond flour, and salt for crust in a bowl.
   
2. Combine sugar, butter, shortening, and almond extract in the bowl of a stand mixer fitted with the paddle attachment; beat until light and somewhat fluffy. Add dry ingredients on low speed until just mixed, about 1 minute; do not overmix.
   
3. Drop dough into a 9x13-inch glass baking dish and flatten with floured hands, building up a 1/2-inch edge on the sides so the filling doesn't stick to the dish. Transfer to the refrigerator to chill for at least 30 minutes.
   
4. Preheat the oven to 350 degrees F (175 degrees C).
   
5. Remove crust from the refrigerator and bake on the center rack of the preheated oven until golden at the edges and pale golden in the center, 45 to 60 minutes. Remove from the oven and let sit on a wire rack until completely cool, about 30 minutes. Reduce oven heat to 300 degrees F (150 degrees C).
   
6. While the crust is cooling, combine sugar, flour, lemon juice, honey, 6 egg yolks, 4 egg whites, lemon zest, and baking soda for filling in a bowl. Whisk briefly to combine, but don't overmix because we don't want to over-aerate the filling. Set aside 2 remaining egg whites for the meringue topping.
   
7. Spread blueberries over the cooled crust, then pour filling over top.
   
8. Bake in the 300 degrees F (150 degrees C) oven, checking frequently, until filling is set, 40 to 50 minutes. Remove from the oven, turn oven off, and let cool to room temperature on a wire rack, about 30 minutes.
   
9. Set an oven rack about 6 inches from the heat source and preheat the oven's broiler to high, or 525 degrees F (274 degrees C).
   
10. Combine 2 reserved egg whites from the filling with 2 egg whites, sugar, cream of tartar, and salt for meringue in the top of a double boiler over simmering water. Whisk frequently, scraping down the sides with a rubber spatula to avoid scorching, until sugar has dissolved and mixture is hot, 2 to 3 minutes.
    
11. Remove egg white mixture from the heat and beat with an electric mixer on medium speed until soft peaks form. Increase speed to high and beat until meringue holds stiff, but spreadable, peaks. Spread and swirl meringue on top of the cooled blueberry bars.
    
12. Set the lemon bars under the preheated broiler until meringue is evenly toasted and golden brown, about 30 to 60 seconds; do not walk away.
    
13. Cut into 24 squares or triangles and refrigerate until chilled, about 3 hours.