Step 1Puree the raspberries in a food mill, discarding the seeds. The raspberries can also be pureed in a food processor, then strained to remove the seeds. This makes about 1 cup puree.
Step 2Place the berries in a medium bowl and whisk in the sugar until dissolved. Stir in the lemon juice and chill until ready to use. This makes a scant 1 1/2 cups syrup and will keep for 3 days, covered and refrigerated.
Step 1Cut a sheet of waxed paper that is long enough to fit around a 1-quart souffle dish and fold it lengthwise in thirds to make a ribbon about 4 inches wide. Wrap this around the top of the dish to make a collar and tape the ends together. The collar should extend about 3 inches above the rim of the souffle dish. Secure in place with a rubber band or tape and place the dish in the freezer to chill. Alternatively, prepare 8 (one-half cup) ramekins in a similar fashion, making sure the collars extend about 1 1/2 inches over the ramekins.
Step 2In a large saucepan, heat the peaches with one-third cup sugar and lemon juice over medium heat. Cook, stirring frequently, until the peaches have softened and broken down into a consistency resembling a loose applesauce, about 15 minutes.
Step 3Puree the cooked peaches in a food mill or blender. You should have about 2 cups.
Step 4Warm the peach liqueur in a small saucepan over medium heat. Stir in the gelatin and cook, stirring, until the gelatin melts. Immediately stir the gelatin mixture and the almond extract into the peach puree and chill until cold.
Step 5Bring a pot of water to a simmer. Beat together the egg yolks and remaining two-thirds cup sugar in a mixing bowl and place the bowl over the simmering water, being careful not to let the bottom of the bowl touch the water. Immediately start whisking the egg yolks and continue until they are quite pale and have approximately doubled in volume, 5 to 7 minutes. When you rub a little of the egg yolk mixture between your fingers, you shouldn't feel any grit from the sugar.
Step 6Remove the bowl from the heat, whisk in the peach mixture and continue whisking until the mixture has cooled.
Step 7Beat the egg whites to stiff peaks in an electric mixer using the whisk attachment. In a separate large bowl, beat the whipping cream to soft peaks with a whisk or hand mixer. Spoon about one-half of the egg whites into the cooled egg yolk mixture and stir to lighten the mixture. Add the remaining egg whites to the whipped cream and pour the peach mixture on top. Gently fold them all together to make a uniform mixture.
Step 8Gently spoon the mixture into the souffle dish or the ramekins. It should come at least halfway up the paper collar. Smooth the top and scatter over the sliced toasted almonds. Freeze until very firm, at least 4 hours. If you freeze it overnight, transfer it to the refrigerator for at least 1 hour to soften before serving. If you make it more than 1 day in advance, once the mixture is frozen solid, cover it with plastic wrap and gently press the wrap against the surface of the souffle.
Step 9When ready to serve, carefully remove the collar. Serve in ramekins or thin slices from the souffle dish with a little raspberry sauce spooned over and the rest passed on the side.