In a large bowl, whisk together butter, sugar and egg yolk.
As soon as the mixture is smooth, add baking powder and flour, in small portions; mix in by using a spatula or hand. Dough will be a bit crumbly, but that is OK.
Break off a part of the dough, cover it with a plastic and roll it out into 1/4 of an inch thickness.
Using a cutter, cut out the size of cookies, based on your preference. Use a knife to lift each cookie, to move it into a baking sheet. Bake them at 350F for 12-15 minutes. Let it cool to a room temperature.
Fill a piping or a ziplock bag with dulce de leche. Pipe the filling onto half of the cookies, and cover them with the other half.
Melt chocolate chips in a microwave, stirring it every few seconds. Add shortening into the melted chocolate to make the chocolate a bit runny.
Dip half of each cookie into chocolate and place the cookie on a baking mat. Sprinkle with crushed almonds and let the chocolate harden.
Keep Dulce De Leche sandwich cookies in a sealed container until ready to serve.