In a small bowl mix together flour, salt and baking powder.
In the large bowl of an electric mixer, beat cannabutter and butter until light and fluffy. Beat in sugar until well combined. Add egg, poppy seeds, lemon zest and lemon extract and mix until just combined.
Divide dough in half and press into two large discs, wrap in plastic wrap and chill for at least 2 hours.
Preheat oven to 325 degrees F. Line two large baking sheets with parchment paper.
On a floured surface, roll out a dough disk to 1/8 inch thickness. Use a 2 1/2 inch round cookie cutter (or the bottom of a small glass) to cut out cookies. Arrange on the prepared baking sheets, 1 inch apart. Gather the scraps and re-roll to make more cookies. Bake for about 20 minutes, or until cookies are just starting to turn brown. Cool on baking sheets for 2 minutes before transferring to a wire rack to cool completely.
Beat all the filling ingredients together until light and fluffy.
Spread a thin layer of filling on the bottom of one cookie and press another cookie, bottom side down, onto the filling.
Chill until ready to serve. Try to assemble the cookies as near to the time when you will be eating them as possible as extended time in the refrigerator will make them lose their crispness.