Like peaches, nectarines can be placed in a paper bag to speed ripening.
Process nectarines and sugar in a food processor 30 to 45 seconds. Transfer to a large bowl; cover and chill 2 hours.
Melt butter over medium-low heat in a medium skillet; add almonds and salt. Cook almonds, stirring frequently, 3 to 5 minutes or until toasted and golden. Pour nut mixture through a fine wire-mesh strainer, shaking to remove excess butter and salt. Stir almonds into nectarine mixture; cover and chill until ready to use.