Preheat oven to 350F. Spray a 9x5x3" loaf pan with cooking spray and set aside.
Whisk together the flour, baking powder, baking soda, and salt in a bowl, set aside. Mix the lemon juice and buttermilk together, set aside.
Cream the butter and initial sugar together in a large bowl of a stand up mixer with a paddle attachment, until light and fluffy, 5 min. Add in the eggs one at a time, mixing well after each. Add in the lemon zest and lemon extract. Add the flour and buttermilk mixture alternatively, starting and ending with the flour. Mix well.
Pour the batter into the prepared loaf pan and bake for 45 min. to 1 hour or until cake tester comes out clean. Let cake cool for 10 min.
Mix together the syrup ingredients and microwave, stirring after 30 seconds and until sugar melts, about 1 min. Remove cake from pan and place on a cooking rack over a rimmed cookie sheet. Brush on the syrup and let the cake cool completely.
When ready to serve, mix the glaze ingredients together and pour over the cake. Decorate with lemon slices if desired.
The cake freezes well at any stage, after the syrup or after the glaze. I slice the cake and put into baggies for lunch box snacks.