Rosehip-Sherry Shortbread Cookies
For the cookies: Combine the ground almonds, flour, cornstarch and vanilla sugar in a large bowl. Add the egg yolk and Sherry and distribute the butter over the top. Mix everything together using a pastry cutter or two forks, then quickly knead with hands to form a smooth dough. Wrap with plastic wrap and refrigerate for 30 minutes.
Preheat the oven to 175°C/160°C convection/gas mark 2 (approximately 350°F/325°F convection). Roll the dough out onto a lightly floured surface to about 2-3 mm (approximately 1/10 inch) thick. Cut into circles about 4 cm (approximately 1.5 inches) in diameter and scalloped circles about 2 cm (approximately 3/4 inch) in diameter. Place the large and small cookies on separate baking sheets lined with parchment paper. Bake the large cookies for 12-15 minutes and the small cookies for 8-10 minutes, until both are golden brown. Remove from the oven and cool on a wire rack.
To decorate: Warm the rosehip jam until thinned, spread onto the large cookies and top with the small cookies. Allow the jam to dry.
Mix the powdered sugar with the Sherry until smooth. Transfer the icing to a freezer bag with the corner tip snipped off and decorate each cookie with a swirl of icing.