Step 1

On day 1, prepare salt & sugar mixture on a plate with spoon-sized indents to fit egg yolks.

Step 2

Separate egg yolks from egg whites and place each yolk into an indent.

Step 3

Carefully cover with the mixture so each yolk is surrounded.

Step 4

Refrigerate salt & egg mixture for 5 days.

Step 5

On day 4, place bone marrow in a brine solution and refrigerate for 3 days.

Step 6

On day 5, remove egg yolks from salt mixture and rinse with water.

Step 7

Place egg yolks on parchment paper and cook on a low temperature for 2 hours then allow to cool.

Step 8

Once cooled, use a grater to shave the cured egg yolk.

Step 9

Remove bone marrow from the brine solution and broil in the oven for 10 minutes then allow to cool.

Step 10

Carefully scoop the center of the bone marrow out using a spoon and set aside in a covered bowl.

Step 11

Place all of the ingredients in a food processor & blend until smooth.

Step 12

Spread plastic sheet onto counter and spoon the mixture into the center.

Step 13

Fold the plastic around the mixture to form a tight tube-shaped package.

Step 14

Allow mixture to rest in plastic packaging for 2 hours in the refrigerator.

Step 15

Remove plastic from butter tube and cut into 1/2 inch-thick slices.

Step 16

Use right away or wrap individual slices in plastic wrap for freezing.