In a mixer with the flat paddle attachment, cream the butter and sugar at medium speed until fluffy, about 2 minutes.

Add the egg, optional orange zest, orange juice, and vanilla; start mixer at a slow speed and then go to a medium high speed to combine well, about 2 minutes.

Next sprinkle the salt, baking powder, and some of the flour into the mixer. Combine on low so the flour doesn't fly and gradually add all the flour. Mix until flour is just incorporated and the dough has mostly come together. Do not overmix.

Divide dough into 4 flat discs and wrap in plastic wrap. Refrigerate for about 1 hour or overnight.

Make space in fridge or freezer for a baking sheet. Line 2 baking sheets with parchment.

Take out 1 disc at a time. Lightly flour a work surface (such as a silicone dough mat) and rolling pin. Roll the chilled dough out to about ⅛" thick.

Using a cookie or ravioli cutter (2-½ to 3 inches in diameter), make dough circles. Alternatively, use the rim of a glass jar or cup to cut the rounds of dough.

Fill and shape the cookie dough circle right on the parchment lined baking sheet. Lift up the edge of each circle on your cutting surface with a small spatula or butter knife and transfer to baking sheet. Space the circles about 1" apart.

Dot the center of each circle with a dollop of filling, about a heaping ½ teaspoon with 2-½ inch circles (a scant teaspoon for 3" circles).

Fold up the sides of the circle to make a triangle-shaped cookie with a small window of filling revealed in the center.

Let the filled cookies chill in the refrigerator for about 15 minutes before baking. While chilling, preheat the oven to 350ºF.

Bake for about 14-17 minutes or until the bottom and edges get a touch of light golden brown.

Let cool on a cooling rack before eating because the filling is hot.