Compound word: midsummer sweetheart (or midsummer date/boyfriend/girlfriend, etc.)
The compound word appears in our example in the partitive singular, juhannusheilaa since it receives the action of the verb hemmottele.
Juhannus is Midsummer, occurring around June 21st, one of the biggest holidays of the year in Finland.
Other words you often see combined with juhannus are juhannussauna (”midsummer sauna”), juhannussää (”midsummer weather”), and juhannusliikenne (”midsummer traffic”).
The newspaper page includes recipes you can make to ”spoil your midsummer sweetheart.”