Ingredients

• 1 cup Unbleached White All-Purpose Flour
• 3/4 cup Almond Flour
• Finely grated zest from 1 Lemon
• 1/4 cup Granulated Sugar
• 4 oz Unsalted Butter at room temperature + 2 Tbsp (for chocolate filing)
• 1 tsp Vanilla Extract
• 4 oz Bittersweet Chocolate broken into small pieces
• 2 tsp Golden Syrup or Light Corn Wyrup
• Sea Salt to taste

Instructions

1. Preheat oven to to 350°F. Line two small baking sheets (or one large one) with parchment paper.
2. In a small bowl, whisk together all-purpose flour and almond meal.
3. In another small bowl, combine lemon zest with sugar. With the tips of your fingers, rub the zest and sugar together until they’re well integrated.
4. Combine the butter and sugar-zest mixture in the bowl of a stand or hand mixer. Beat them together on medium speed until light and fluffy, about 3 minutes, stopping once or twice to scrape down the sides of your bowl with a rubber spatula. Add the vanilla extract and beat for a few more seconds. Reduce the mixer speed to low, then add the almond meal-flour mixture a little at a time. Beat just until just incorporated into the dough, but don’t overmix.
5. Scoop teaspoon-sized balls of dough (a melon scoop works well) and roll them to form small balls. Place the balls about 2 inches apart on the parchment-lined baking sheets. Using your thumb, make an indentation in the center of each cookie. Make sure you don't press through the dough, but make sure the centers are plenty deep and wide to hold the chocolate filling.
6. Bake about 15 minutes, or until the cookies are only slightly colored around the edges; be careful to not overbake. (About 10 minutes in, I often check the thumbprint indentations—if they seem too shallow, remove the cookie sheet and depress the centers while the dough is still soft. The curved back of a melon scoop or teaspoon works well.) When done, remove the baking sheets from oven and transfer the cookies to cooling racks.
7. To make chocolate filling: using a double boiler or a small heat-proof bowl set over a pot of simmering water, combine chocolate, 2 tablespoons butter and golden syrup. Stir until melted and smooth. Cool slightly. When cookies are cool, fill the thumbprints with the chocolate mixture and then sprinkle with sea salt. Allow about an hour for the chocolate centers to set.