Heat <quantity>4<unit>cups</unit></quantity> of water in a saucepan until it reaches <temperature>71<unit>°C</unit></temperature>

Add <quantity>3<unit>cups</unit></quantity> of katsuobushi

Remove from the heat and let it infuse for 10m

Strain the katsuobushi. The katsuo dashi is ready

Add <quantity>3<unit>cups</unit></quantity> of the dashi to a pan over medium heat

Add <quantity>½<unit>cup</unit></quantity> of soy sauce

Add <quantity>¼<unit>cup</unit></quantity> of sake. Bring to a simmer

Add <quantity>1<unit>tbsp</unit></quantity> of white sugar and stir to dissolve

Remove from the heat and let it cool at room temperature. The tsuyu is ready

Use it to make your favorite udon!