In the bowl of the stand mixer with a paddle attachment, cream the butter and sugar, 3-4 minutes. Scrape down the sides of the bowl and add the eggs (one at a time) with the mixer running on low. Pour in the extract, peach syrup, sourdough discard and mix until everything is well combined. Scrape down the sides of the bowl again, and sprinkle over half of the dry ingredients. Give it a stir, then add the rest of the dry ingredients. Once the last bits of flour are incorporated, quickly pour in the milk and give the batter one last stir.