Pour <quantity>1<unit>cup</unit></quantity> of vegetable oil into a blender

Add <quantity>½<unit>cup</unit></quantity> of dried used coffee grounds

Blend on low speed and gradually increase to high until grounds are pulverized

Extract the coffee flavor at room temperature for 1d

Pour oil through fine sieve just until the sediment starts to come out. The coffee oil is ready

Peel <quantity>4<unit>kg</unit></quantity> of waxy potatoes

Transfer potatoes to a large pot and cover with cold water

Bring to a boil on medium heat. Reduce heat to low and simmer until potatoes are cooked through but not falling apart. Remove

Remove potatoes. Cool in the refrigerator until they reach room temperature

Place potatoes into a sterilized fermentation vessel

Whisk <quantity>160<unit>g</unit></quantity> of salt into <quantity>4<unit>l</unit></quantity> of water until fully dissolved

Add <quantity>1<unit>g</unit></quantity> of lactobacillus starter and whisk to incorporate

Pour water mixture over potatoes to cover. Seal fermentation vessel

Keep fermentation vessel at constant ambient temperature and in good sanitary conditions for 4d, until potatoes ferment

Remove a potato from vessel and check the pH. The pH should be under 4, preferably between 3.2-3.9. If it does not reach the desired pH, ferment for 1 more day under the same conditions

If you do not have a pH reader, you can taste the potatoes. The umami should be pronounced with a pleasant acidity. If there are green or black growths or if it smells off, do not consume

The fermented potatoes are ready

Set aside <quantity>½</quantity> fermented potato . Dice the rest into <quantity>1<unit>cm</unit></quantity> pieces

Add <quantity>225<unit>g</unit></quantity> of all-purpose flour to a bowl

Add <quantity>50<unit>g</unit></quantity> of sugar

Add <quantity>5<unit>g</unit></quantity> of salt

Add <quantity>3<unit>g</unit></quantity> of baking powder

Add <quantity>200<unit>ml</unit></quantity> of milk and mix

Add <quantity>100<unit>ml</unit></quantity> of water and mix

Add <quantity>2</quantity> eggs. Mix to incorporate

Add <quantity>200<unit>g</unit></quantity> of coffee oil and mix

Melt <quantity>100<unit>g</unit></quantity> of quality butter in a pot on low heat

Slowly drizzle the melted butter into the batter while continuously mixing

Grate the <quantity>½</quantity> fermented potato into the bowl

Add the remained fermented potatoes and mix

Let the batter rest in the refrigerator for 30m

Preheat a waffle iron to medium/high while batter is resting

Scoop the batter and distribute evenly

Cook the waffles until they are deep golden brown

The Fermented Potato Waffles are ready to be enjoyed!!