Preheat the oven to 325° and line a baking sheet with a silicone baking mat or parchment paper.

In a large bowl, whisk together the almond flour, sweetener, baking powder, and salt. Stir in ¼ cup melted butter, egg, and almond extract until the dough comes together.

Turn the dough out onto the prepared baking sheet and form into a low, flat log, about 10 x 4 inches. Brush with the remaining 1 tablespoon of melted butter and firmly press the sliced almonds into the top.

Bake 22 to 25 minutes, until lightly browned and just firm to the touch. Remove from the oven and let cool 30 minutes. Reduce the oven temperature to 250F.

Using a sharp knife, cut the log crosswise into 12 slices. (A straight up and down motion works better than sawing back and forth). Place the slices back on the baking sheet. Bake another 15 minutes, then carefully flip them over. Turn off the oven and let the biscotti sit inside until cool.