Start by preheating your oven to 350°F so it reaches the proper temperature by the time your dough is ready. While the oven heats, gather all ingredients and measure them out—this is especially important with gluten-free baking since precision matters more. Soften your butter to room temperature (it should be soft enough to leave a slight indentation when pressed but not melting or greasy), and separate your egg yolk from the white, setting the yolk aside for the egg wash later.

In one bowl, whisk together your gluten-free flour blend, xanthan gum (if your blend doesn't contain it), and kosher salt to evenly distribute these dry ingredients and prevent clumping in the final dough. In a separate bowl, whisk together the whole egg, vanilla extract, and almond extract—this creates a homogeneous wet mixture that will incorporate smoothly into the butter and sugar.

Beat the softened butter and granulated sugar together for 2-3 minutes until light and fluffy—this creaming process incorporates air and creates a tender cookie texture. Gradually add the wet ingredient mixture from Step 2 while mixing on medium speed, scraping down the bowl as needed to ensure everything combines evenly. Finally, add the dry ingredient mixture from Step 2 and mix on low speed just until the dough comes together; I prefer to use a spatula at the end to hand-mix slightly to avoid overdeveloping gluten and to ensure all dry pockets are incorporated without making the dough tough.

Refrigerate your dough for 10 minutes to make it firmer and easier to work with—this prevents the dough from sticking to your hands and helps the cookies hold their shape during baking. While the dough chills, prepare your baking sheets with parchment paper and set them nearby. After chilling, roll the dough into 1-inch balls and place them about 1 inch apart on your prepared baking sheets.

Working with one ball at a time, use your thumb or the back of a small measuring spoon to press a gentle indent into the center of each dough ball, creating a small well without pressing all the way through to the bottom. Spoon about 1/2 teaspoon of jam into each thumbprint—I recommend using a small measuring spoon or piping bag for consistent filling amounts. Don't overfill, as jam can spread during baking.

Place the filled cookie sheets into your preheated 350°F oven and bake for 8-10 minutes, until the edges are just turning light golden brown but the centers still look slightly underdone. The cookies will continue to cook slightly on the hot pan after removal from the oven. Let them cool on the baking sheet for 2-3 minutes to firm up slightly, then transfer them to a cooling rack to cool completely before adding the chocolate drizzle.

Once cookies have cooled completely, combine your white chocolate chips and vegetable shortening in a microwave-safe bowl. Microwave in 30-second intervals, stirring between each interval, until fully melted and smooth—the shortening helps thin the chocolate slightly for easier drizzling and creates a silky texture. Let the chocolate cool for about 5 minutes so it's warm but not piping hot, then drizzle it over each cooled cookie using a fork or small spoon. Allow the chocolate to set at room temperature for about 15-20 minutes before serving.