Preheat oven to 350 degrees F. Grease and line a 9x9-inch pan with parchment, leaving a 2-inch overhang on the sides.
Make the crust: In the bowl of a stand mixer fitted with the paddle attachment or in a large bowl using a hand mixer, beat the butter and granulated sugar on medium speed until light and fluffy, about 5 minutes. Add the egg and vanilla extract and beat until combined.
In a separate bowl, whisk together flour, baking powder, and salt. Add dry ingredients to the butter mixture and mix on low speed until combined.
Transfer the dough into the prepared pan and use your fingers or the flat bottom of a measuring cup to press the dough evenly into the bottom of the pan. Use a fork to poke a few holes into the crust and bake for 15 minutes. Place the pan on a wire rack to cool while making the filling.
Make the filling: Combine the butter, honey, light brown sugar, and zests in a medium, heavy-bottomed saucepan. Cook over medium heat, whisking until the butter has melted. Bring to a boil and then cook for 3 minutes, stirring frequently. Remove the saucepan from the heat and stir in the heavy cream and vanilla extract. Stir in the chopped pecans and mix to combine.
Pour mixture over the crust and spread it evenly. Bake for 20-30 minutes, or until the filling has thickened (filling will continue to set as it cools). Transfer the baking pan to a wire rack to cool completely.
Once completely cool, use the parchment paper to lift out of the pan and cut into bars.
Optional: Dip the bars or drizzle with melted dark chocolate and then top with flaked sea salt.