In a small skillet over medium-high heat, cook the tasso, stirring, until the fat is rendered. Remove from the pan and drain on paper towels, reserving the fat.
In the top of a double boiler, or in a bowl set over a pan of simmering water, beat the egg yolks and lemon juice until pale and thick. Combine the butter and the rendered tasso fat, and whisking constantly, add to the egg mixture in a steady stream. Season with the salt and pepper and continue whisking until thick. Remove from the heat, fold in the tasso, and cover to keep warm until ready to serve.