Cheesy Salmon Rotini - butter

Ingredients

• 3 Tbsp. butter
• 3 Tbsp. all-purpose flour
• 1 tsp. salt
• 1 tsp. dry mustard
• 1 (14 3/4 oz.) can salmon, drained and juice reserved, skin and bones removed or 2 (6 1/2 oz.) cans tuna, drained and flaked*
• milk
• 2 1/2 c. (10 oz.) shredded Wisconsin Colby or Cheddar cheese
• 1 (1 lb.) pkg. Creamettes rotini, uncooked
• 3 Tbsp. softened butter
• 2 to 4 green onions, cut into 2-inch long thin strips