Lower the oven rack to the lower-third position and preheat the oven to 350°F (177°C). Grease an 8.5×4.5-inch loaf pan (like this one or this one) with nonstick spray.

Place the pistachios, along with 1 Tbsp of the flour, in a small food processor. Pulse until the pistachios are finely chopped/coarsely ground. Stop before the pistachios turn into fine crumbs.

In a medium bowl, whisk the ground pistachios with the remaining flour, baking powder, and salt. Set aside.

In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter, sugar, and lemon zest on medium-high speed until the mixture is light and creamy, about 3 minutes. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) With the mixer running on low speed, add the eggs one at a time. Once the second egg is completely incorporated, stop the mixer. Add the sour cream, lemon juice, vanilla, and almond extract, then beat on medium speed until combined. Stop and scrape down the sides and bottom of the bowl as needed. The mixture may look curdled—that’s ok.

Add the dry ingredients to the wet ingredients and beat on low speed until just combined. Avoid over-mixing. If needed, finish mixing by hand to ensure everything is combined. Batter is thick. Pour/spoon the batter into the prepared pan and smooth the top.

Bake for 65–75 minutes, tenting loosely with aluminum foil halfway through baking to prevent over-browning. The cake is done when a toothpick inserted in the center comes out mostly clean with just a few moist crumbs. Baking times vary, so keep an eye on yours and don’t be alarmed if yours is taking longer.

Allow the cake to cool in the pan set on a cooling rack for 1 hour. Carefully remove the cake from the pan and set it directly on the rack. Set the rack over a sheet of parchment paper or a baking sheet. You can add the icing while the cake is still slightly warm or wait for it to cool completely.

In a medium bowl, whisk together the sifted confectioners’ sugar, lemon juice, and cream/milk. Pour the icing over the cake. Sprinkle with chopped pistachios, if using. Allow the cake to cool completely before slicing, which promises neater slices. The icing will set within a couple of hours.

Cover and store leftover cake at room temperature for up to 3 days, or in the refrigerator for up to 1 week.