Preheat oven to 350°F. Grease an 8-inch square pan with baking spray or butter, and line all sides with parchment paper (leaving a 1-inch overhang on each side). Grease the paper as well.
Beat butter, sugar, and salt on medium speed in the bowl of a stand mixer fitted with the paddle attachment 2 minutes or until light and fluffy. Add flour, and mix on low speed until just combined.
Press dough (the dough will be slightly dry) into the bottom and 1/2-inch up the sides of prepared pan. Prick all over with fork, and bake 15 to 20 minutes or until the edges are slightly golden.
Meanwhile, whisk egg yolks, condensed milk, lemon juice, honey, and lemon zest until smooth. Pour over hot crust in pan, and bake 25 to 30 minutes or until filling is set.
Cool lemon bars completely in pan before transferring pan to refrigerator to chill at least 2 hours or up to 3 days.
Lift bars from pan using parchment paper overhang and cut into squares. Dust with powdered sugar and garnish with lemon slices, if desired.