Peel broccoli stems, then coarsely chop stems and florets. Cook broccoli in boiling salted water (1 1/2 tsp salt in 4 qts. of water) until just tender, 4-6 minutes. Drain in a colander and run under cold water to stop cooking.
Simmer cream, garlic, nutmeg, 1/4 tsp salt and 1/8 teaspoons pepper in a medium saucepan, uncovered, until slightly thickened and reduced to about 2/3 cup, about 5 minutes.
Add broccoli and simmer, mashing with a potato masher, until coarsely mashed and heated through, about 2 minutes.
Remove from heat and stir in parmesan and lemon juice.