Grease a 9x13-inch pan. In a large pot over low heat, melt the butter, then add the marshmallows and salt. Stir until just melted and smooth, about 5 minutes. Remove from heat and stir in the almond and vanilla extracts.

Fold in the Rice Krispies until evenly coated. Add 3 tbsp sprinkles and fold briefly to distribute.

Press the mixture firmly into the prepared pan. Scatter the remaining 1 tbsp sprinkles on top and press them in lightly. Cool completely, then slice into 16 squares.