1. Preheat the oven to 400ºF (200ºC).
2. Line a 9-inch (23cm) square baking pan with aluminum foil, easing it up the insides of the pan. Spray the foil with nonstick spray or lightly grease it with a bit of softened butter.
3. To make the crust, add the almond flour, all-purpose flour, 3 tablespoons sugar, and salt to the bowl of a food processor. Pulse a few times, then add the 6 tablespoons (90g) of cubed butter and pulse until the mixture resembles very coarse cornmeal. Add the egg yolk, water, and vanilla and process until the dough comes together. If it’s too dry, add another tablespoon of water.
(You can also make the dough by hand, cutting the butter into the dry ingredients with a pastry blender or a fork.)
4. Press the dough into the pan so it covers the bottom evenly. Bake the dough until the top is golden brown, about 12 minutes.
5. While the dough is baking, make the topping by melting the 4 tablespoons (60g) butter in a small saucepan. Once it has melted, add the sugar, honey, orange zest, vanilla, and salt, stirring until smooth. Remove from heat and add the sliced almonds, stirring until they’re completely coated with the butter-honey mixture.
6. Scrape the almond mixture onto the still warm baked crust and spread it evenly over the top. Bake for 10 to 12 minutes more, or until the almond topping is nicely bronzed. Let cool. Remove from the pan by lifting out the foil. Cut into squares or rectangles.