Jammy Shortbread Bars
Servings: Makes 16 large bars or 32 mini bars
2 sticks (226g) salted butter, at room temperature
½ cup (106g) light brown sugar
1½ teaspoons pure vanilla extract
2½ cups (301g) all-purpose flour
¼ teaspoon fine sea salt
1½ cups (510g) seedless raspberry jam
2 large (71g) egg whites
¼ teaspoon cream of tartar
¾ cup (149g) granulated sugar
2 sticks (226g) unsalted butter, at room temperature
1 teaspoon pure vanilla extract
Freeze-dried raspberries, as needed for finishing (optional)
1. Make the Shortbread: Preheat the oven to 350°F. Grease a 9-inch-by-13-inch pan with nonstick spray, then line with parchment paper, leaving about 2 inches of excess paper on both sides.
2. In the bowl of an electric mixer fitted with the paddle attachment, cream the butter and brown sugar until light and fluffy, about 5 minutes. Add the vanilla and mix to combine.
3. Add the flour and salt, and mix on low speed to combine. Scrape the side of the bowl and mix once more. Transfer the dough into the prepared pan and use damp hands to press it into an even layer. Bake the shortbread crust until golden brown at the edges and set across the surface, 20 to 24 minutes. Cool completely.
4. Spoon the jam onto the center of the shortbread and then spread it into a very thin, even layer, leaving the outer ¼ inch of the shortbread uncovered. Transfer to the freezer while you make the frosting.
5. Make the Frosting: Fill a medium saucepan with 2 inches of water and bring it to a simmer over medium-low heat. Set a medium bowl over the pot, add the egg whites, cream of tartar and sugar, and whisk to combine. Heat, whisking constantly, until the mixture reaches 160°F on a thermometer.
6. Remove the bowl from the heat and transfer to the bowl of a stand mixer fitted with the whip attachment. Whip the mixture on medium-high speed until it reaches stiff peaks and the bowl is no longer warm to the touch, about 4 minutes.
7. Add the softened butter 1 tablespoon (14g) at a time and whip until well combined, about 4 minutes total. Add the vanilla and mix to combine.
8. Remove the shortbread from the freezer and dollop the frosting evenly over the surface, then use a small spatula to spread it into an even, swoopy layer. Sprinkle with freeze-dried raspberries (if using), then transfer to the refrigerator for 10 minutes (this makes the bars easier to slice).
9. Use the excess parchment to lift the bars out of the pan, then slice into 16 large bars or 32 mini bars. For the cleanest slices, wipe the knife clean between cuts.