Position a rack in the center of the oven and preheat to 350°F. Line 2 baking sheets with parchment paper or silicone baking mats. If neither is available, lightly grease the baking sheets with a little of the shortening.

Place the 1 cup almonds in the bowl of a food processor and grind until finely ground; transfer the ground almonds to a shallow bowl and set aside.

In a medium bowl, whisk together the 1 1/4 cups quick cooking rolled oats, 1 cup unbleached all purpose flour, and 1/4 teaspoon salt. Set this dry oat mixture aside.

In the bowl of an electric mixer fitted with the paddle attachment, beat 6 tablespoons softened unsalted butter, 1/2 cup solid vegetable shortening (Crisco), and 1/2 cup packed brown sugar on medium speed until the mixture is light and creamy, about 2–3 minutes.

Add the large egg yolk and 2 teaspoons vanilla extract to the butter mixture and beat until well blended, scraping down the sides of the bowl as needed.

On low speed, add the reserved dry oat mixture to the wet mixture and mix until just combined. If time permits, let the dough rest 15–30 minutes to firm slightly.

Using your fingers, pinch off portions of dough and roll into 1-inch balls. Roll each ball in the ground almonds, coating completely.

Place the almond-coated dough balls on the prepared baking sheets about 1 1/2 inches apart. Flatten each ball slightly with the palm of your hand.

Press your thumb into the center of each cookie to form a thumbprint indentation. If the indentation distorts the round edge, gently push the edges back together to maintain a round shape.

Spoon about 1/2 teaspoon of the Forest Berries jam into the indentation of each cookie.

Bake one sheet at a time on the center rack for 14–16 minutes, until the cookies are golden brown. Remove the sheet from the oven and transfer the cookies to a wire rack to cool completely.