Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
In a mixing bowl, cream the softened butter and granulated sugar together until light and fluffy.
Beat in the egg and vanilla extract until well combined.
In a separate bowl, whisk together all-purpose flour, almond flour, salt, and baking powder.
Gradually add the dry ingredients to the butter mixture, mixing until just combined.
Use your hands to form small balls (about 1 inch in diameter) from the dough and arrange them on the prepared baking sheets, spacing them about 2 inches apart.
With your thumb or the back of a small spoon, gently press down in the center of each dough ball to create an indentation.
Fill each thumbprint with raspberry jam, making sure not to overfill.
Sprinkle sliced almonds over the top of each cookie for added texture and flavor.
Bake in the preheated oven for 12-15 minutes, or until the edges are lightly golden.
Allow cookies to cool on the baking sheets for 5 minutes before transferring them to wire racks to cool completely.
Notes
Make sure not to overfill the thumbprints with jam.