Place the cubed pears, cremant, rosemary and cassava in a sauce pan on medium high heat. Bring to a boil and then turn down the temperature to low and simmer for 7 minutes to soften the pears. It should not be mushy, just soft.
Make the Jelly
Strain out the rosemary and pears. Throw out the rosemary and place the pears in 4 glasses.
Place the cremant poaching liquid back in the pan and add in the 2 Tablespoons of agar agar flakes. Bring to a low boil for 5 minutes. Then take off the heat and pour into the 4 glasses with the pears.
Garnish with small sprigs of rosemary flowers and refrigerate for 20 minutes until set.