Preheat oven to 350° F. Grease a 9"x5" loaf pan (see note) and line with parchment (see note). Set aside.
In a small bowl, combine the dry ingredients (flour, baking powder, and salt). Set aside.
In the bowl of a stand mixer, combine the sugar and the lemon zest. Be sure to only use the yellow part of the rind and not the bitter white pith underneath. Run the mixer on low for a few minutes to allow the oils from the lemon zest to release into the sugar.
Add the butter and cream together until light and fluffy (at least 3 minutes). Add the eggs, one at a time, followed by the lemon extract paste (see note), scraping down the sides of the bowl as needed.
Alternate additions of the dry ingredients and the buttermilk: half the dry ingredients, followed by the buttermilk, then the remaining dry ingredients. Mix until nearly incorporated.
Toss the blackberries in a tablespoon of flour to coat them. This will help to suspend them in the batter so they don't just sink to the bottom of the bread. Gently fold the blackberries into the batter by hand, taking care not to break them apart.
Pour the batter into the prepared pan and smooth the top with a spatula. Bake until golden and a toothpick inserted in the center comes out with just a few moist crumbs attached, about 75 minutes. Allow bread to cool in the pan at least 15 minutes before removing to a wire rack to cool completely.
For Glaze
In a medium saucepan, combine the blackberries, lemon zest, lemon juice, water, and sugar. Cook over medium-low heat. Once the mixture is bubbling, cook for an additional five minutes, or until the berries break down. You can hasten this process a bit by smushing (it's a technical term) the berries with a spatula.
Strain the mixture (you may want to let it cool a bit first) to remove the seeds and pulp. Return the blackberry juice mixture to the saucepan.
Over medium-low heat, cook until the liquid is reduced to about ¼ cup (5-7 minutes). Make sure to check/stir frequently, as the more the liquid reduces, the more likely it will burn. Take the saucepan off the heat and allow the mixture to cool slightly.
In a medium bowl, combine the sifted powdered sugar with the blackberry reduction. Stir until all the powdered sugar is incorporated. Add 1 tablespoon of cream and mix until smooth. If the glaze is too thick, you can add a bit more cream. If it's too thin, you can add a bit more powdered sugar.
Pour the glaze over the cooled bread. Top with fresh blackberries, if desired. Allow the glaze to set up before serving.
The baked and glazed bread will keep, wrapped well, for up to three days on your kitchen counter. (In fact, I think the texture is better on the second day!)The plain bread (without glaze) can also be well wrapped and frozen for up to three months. I suggest waiting to make the glaze until you'd like to use it, as it sets up over time and won't be pourable.Enjoy!
Notes
Note on lemon extract paste: For a punch of lemon flavor without adding much liquid! If you'd like, you can substitute with an equal measure of lemon extract.Note on buttermilk: For best results, I do suggest that you use buttermilk! That said, you can make a quick substitution if you don't have it on-hand. For this recipe, put ½ teaspoon vinegar or lemon juice into a liquid measuring cup, then add enough milk (I find that 2% milkfat or greater works best) to come up to the ½ cup line. Stir, let sit for 5 minutes, then it's ready for use!Note on parchment paper: Lining your pan with parchment makes it easier to remove the pound cake later! I buy pre-cut nonstick parchment sheets that work really well. If you’re interested in checking them out, you can find them here.Note on pan: I used a 9"x5" loaf pan for my bread. If you choose a larger or smaller pan, the bake time will be different!