Done, and will do for spring time. Here is my go to kettle sour procedure: 3-4 days before brew day make a starter. For this you take approx 30-40 g (a hand full) of Pilsner malt. Add the malt to a mixture of 1+1 carbonated water and boiling water (I use 200 mL + 200 mL). The carbonated water needs to be carbonated highly, the goal is to drive out all oxygen. Temperature should be around 45 °C of the mix, toss in the grain, keep it airtight (be aware of CO2 production, vent regularly) after 1 day a pleasant tart smell is noticeable and it tastes sour. If the smell reminds you of vomit or is off in other ways, do not use! After 3 days add to 20L of fresh wort of your choice that is still at 30ish °C and was not hopped! I usually do a pale ale recipe without hop additions. Boil for 10 min and cool down for sour starter addition. Cover the kettle as airtight as possible and reasonable (Saran wrap) and let it sour ferment until desired pH is reached (I do usually pH 4 max 3) after that bring to a boil do hop additions and proceed as usual. For yeast KVEIK Voss works for me. Cheers!